stdlib: Implement mbrtoc8, c8rtomb, and the char8_t typedef.

This change provides implementations for the mbrtoc8 and c8rtomb
functions adopted for C++20 via WG21 P0482R6 and for C2X via WG14
N2653.  It also provides the char8_t typedef from WG14 N2653.

The mbrtoc8 and c8rtomb functions are declared in uchar.h in C2X
mode or when the _GNU_SOURCE macro or C++20 __cpp_char8_t feature
test macro is defined.

The char8_t typedef is declared in uchar.h in C2X mode or when the
_GNU_SOURCE macro is defined and the C++20 __cpp_char8_t feature
test macro is not defined (if __cpp_char8_t is defined, then char8_t
is a builtin type).

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

40 files changed, 360 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index dbf351b895..df882ec243 100644
--- a/NEWS
+++ b/NEWS
@@ -51,6 +51,15 @@ Major new features:
   Previously, input bytes not within the ASCII range resulted in
   unpredictable output.
 
+* Support for the mbrtoc8 and c8rtomb multibyte/UTF-8 character conversion
+  functions has been added per the ISO C2X N2653 and C++20 P0482R6 proposals.
+  Support for the char8_t typedef has been added per the ISO C2X N2653
+  proposal.  The functions are declared in uchar.h in C2X mode or when the
+  _GNU_SOURCE macro or C++20 __cpp_char8_t feature test macro is defined.
+  The char8_t typedef is declared in uchar.h in C2X mode or when the
+  _GNU_SOURCE macro is defined and the C++20 __cpp_char8_t feature test macro
+  is not defined (if __cpp_char8_t is defined, then char8_t is a builtin type).
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * Support for prelink will be removed in the next release; this includes
diff --git a/sysdeps/mach/hurd/i386/libc.abilist b/sysdeps/mach/hurd/i386/libc.abilist
index 4dc87e9061..66fb0e28fa 100644
--- a/sysdeps/mach/hurd/i386/libc.abilist
+++ b/sysdeps/mach/hurd/i386/libc.abilist
@@ -2289,6 +2289,8 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 close_range F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.4 __confstr_chk F
 GLIBC_2.4 __fgets_chk F
 GLIBC_2.4 __fgets_unlocked_chk F
diff --git a/sysdeps/unix/sysv/linux/aarch64/libc.abilist b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
index 16d34b55c6..516b029d30 100644
--- a/sysdeps/unix/sysv/linux/aarch64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
@@ -2616,10 +2616,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/alpha/libc.abilist b/sysdeps/unix/sysv/linux/alpha/libc.abilist
index 3f794bea0f..dde08899fe 100644
--- a/sysdeps/unix/sysv/linux/alpha/libc.abilist
+++ b/sysdeps/unix/sysv/linux/alpha/libc.abilist
@@ -2713,10 +2713,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/arc/libc.abilist b/sysdeps/unix/sysv/linux/arc/libc.abilist
index 072627810c..ade44d3029 100644
--- a/sysdeps/unix/sysv/linux/arc/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arc/libc.abilist
@@ -2377,10 +2377,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/arm/be/libc.abilist b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
index dbd5f07e6e..98b33708af 100644
--- a/sysdeps/unix/sysv/linux/arm/be/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
@@ -496,10 +496,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/arm/le/libc.abilist b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
index 0f02d79faa..05dbbe5bcc 100644
--- a/sysdeps/unix/sysv/linux/arm/le/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
@@ -493,10 +493,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/csky/libc.abilist b/sysdeps/unix/sysv/linux/csky/libc.abilist
index 11d3b36a78..430a24349e 100644
--- a/sysdeps/unix/sysv/linux/csky/libc.abilist
+++ b/sysdeps/unix/sysv/linux/csky/libc.abilist
@@ -2652,10 +2652,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/hppa/libc.abilist b/sysdeps/unix/sysv/linux/hppa/libc.abilist
index 5caa1321b1..de44616526 100644
--- a/sysdeps/unix/sysv/linux/hppa/libc.abilist
+++ b/sysdeps/unix/sysv/linux/hppa/libc.abilist
@@ -2601,10 +2601,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/i386/libc.abilist b/sysdeps/unix/sysv/linux/i386/libc.abilist
index 276d7d5619..18b4fbf26e 100644
--- a/sysdeps/unix/sysv/linux/i386/libc.abilist
+++ b/sysdeps/unix/sysv/linux/i386/libc.abilist
@@ -2785,10 +2785,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/ia64/libc.abilist b/sysdeps/unix/sysv/linux/ia64/libc.abilist
index 5e2249518e..a8e959d417 100644
--- a/sysdeps/unix/sysv/linux/ia64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/ia64/libc.abilist
@@ -2551,10 +2551,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
index 802469a5b9..3a7e4ef6e4 100644
--- a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
+++ b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
@@ -497,10 +497,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
index 2f949397df..864ad2cdf8 100644
--- a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
+++ b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
@@ -2728,10 +2728,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist
index f63cc9cd4c..163058420d 100644
--- a/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist
+++ b/sysdeps/unix/sysv/linux/microblaze/be/libc.abilist
@@ -2701,10 +2701,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist
index 88d2b707f9..a6debfda56 100644
--- a/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist
+++ b/sysdeps/unix/sysv/linux/microblaze/le/libc.abilist
@@ -2698,10 +2698,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
index 6c2bc0ee78..2b53d888de 100644
--- a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
+++ b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
@@ -2693,10 +2693,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
index 09c9980d95..849aae4130 100644
--- a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
+++ b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
@@ -2691,10 +2691,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
index 763920ea8f..37f6c1bf58 100644
--- a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
+++ b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
@@ -2699,10 +2699,12 @@ GLIBC_2.35 __memcmpeq F
 GLIBC_2.35 _dl_find_object F
 GLIBC_2.35 epoll_pwait2 F
 GLIBC_2.35 posix_spawn_file_actions_addtcsetpgrp_np F
+GLIBC_2.36 c8rtomb F
 GLIBC_2.36 fsconfig F
 GLIBC_2.36 fsmount F
 GLIBC_2.36 fsopen F
 GLIBC_2.36 fspick F
+GLIBC_2.36 mbrtoc8 F
 GLIBC_2.36 mount_setattr F
 GLIBC_2.36 move_mount F
 GLIBC_2.36 open_tree F
diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist b/sysdeps/unix/sysv/linu