C23 adds once_flag, ONCE_FLAG_INIT and call_once to stdlib.h (in C11
they were only in threads.h, in C23 they are in both headers; this
change came from N2840).  Implement this change, with a
bits/types/once_flag.h header for the common type and initializer
definitions.

Note that there's an omnibus bug (bug 33001) that covers more than
just these missing definitions.

This doesn't seem a significant enough feature to be worth mentioning
in NEWS.

ISO C is not concerned with whether functions are in libc or
libpthread, but POSIX links this to what header they are declared in,
so functions declared in stdlib.h are supposed to be in libc.
However, the current edition of POSIX is based on C17; hopefully Hurd
glibc will have completed the merge of libpthread into libc (in
particular, moving call_once) well before a future edition of POSIX
based on C23 (or a later version of ISO C) is released.

Tested for x86_64 and x86.

Vector variants of the new C23 log10p1 routines.

Note: Benchmark inputs for log10p1(f) are identical to log1p(f)

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

Vector variants of the new C23 log2p1 routines.

Note: Benchmark inputs for log2p1(f) are identical to log1p(f).

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

rlim_t is 64b on 64b systems, so we should extend RLIM_INFINITY to that,
not only RLIM64_INFINITY or requiring 64b offsets.

This is similar to Linux headers.

Vector variants of the new C23 exp2m1 & exp10m1 routines.

Note: Benchmark inputs for exp2m1 & exp10m1 are identical to exp2 & exp10
respectively, this also includes the floating point variations.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

Add constants indicating the maximum values of speed_t and baud_t.
Hopefully if and when the baud_t interface is standardized then
BAUD_MAX will be included in the standardization from the start.

Historically, the __MAX_BAUD symbol has indicated the maximum speed_t
value on at least some platforms (including glibc).  However, this
name would be problematic for future standardization, because it
confusingly implies a reference to baud_t, not speed_t, and it is
inconsistent with other limit symbols, which are all of the form *_MAX
(e.g. SIZE_MAX for size_t.)

[ v3: dropped leading underscores, leave __MAX_BAUD outside
      #ifdef __USE_MISC since it is a legacy symbol, and
      namespace-protected with a double underscore.
      (Collin Funk, Adhermerval Zanella Netto) ]

[ v4: moved from __USE_MISC to __USE_GNU (Collin Funk) ]

Signed-off-by: "H. Peter Anvin" (Intel) <hpa@zytor.com>
Reviewed-by: Collin Funk <collin.funk1@gmail.com>

The generic code has __ispeed and __ospeed; Linux has c_ispeed and
c_ospeed. Use an anonymous union member to allow both set of names on
all platforms.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Now all platforms unconditionally use the "sane" definitions of the
termios baud constants. Unify them into a common file.

Note: I have made them explicitly unsigned to avoid problems with
compiler warnings for comparisons of unequal signedness or
similar. These constants were historically octal on most platforms,
and so unsigned by default.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

POSIX requires that speed_t is an unsigned integer type, so change the
generic speed_t definition to be an unsigned int instead of a plain
int.

Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Implement double and single precision variants of the C23 routine atan2pi
for both AdvSIMD and SVE.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>