C23 makes various standard library functions, that return a pointer
into an input array, into macros that return a pointer to const when
the relevant argument passed to the macro is a pointer to const.  (The
requirement is for macros, with the existing function types applying
when macro expansion is suppressed.  When a null pointer constant is
passed, such as integer 0, that's the same as a pointer to non-const.)

Implement this feature.  This only applies to C, not C++, since such
macros are not an appropriate way of doing this for C++ and all the
affected functions other than bsearch have overloads to implement an
equivalent feature for C++ anyway.  Nothing is done to apply such a
change to any non-C23 functions with the same property of returning a
pointer into an input array.

The feature is also disabled when _LIBC is defined, since there are
various places in glibc that either redefine these identifiers as
macros, or define the functions themselves, and would need changing to
work in the presence of these macro definitions.  A natural question
is whether we should in fact change those places and not disable the
macro definitions for _LIBC.  If so, we'd need a solution for the
places in glibc that define the macro *before* including the relevant
header (in order in effect to disable the header declaration of the
function by renaming that declaration).

One testcase has #undef added to avoid conflicting with this feature
and another has const added; -Wno-discarded-qualifiers is added for
building zic (but could be removed once there's a new upstream tzcode
release that's const-safe with this C23 change and glibc has updated
to code from that new release).  Probably other places in glibc proper
would need const added if we remove the _LIBC conditionals.

Another question would be whether some GCC extension should be added
to support this feature better with macros that only expand each
argument once (as well as reducing duplication of diagnostics for bad
usages such as non-pointer and pointer-to-volatile-qualfied
arguments).

Tested for x86_64.

The count_leading_zeros is not used anymore, so there is no need to
provide the table for possible usage.  The hppa already provides
the compat symbol on libgcc-compat.c.

Reviewed-by: Collin Funk <collin.funk1@gmail.com>

The C2y function uimaxabs has been renamed to umaxabs.  Implement this
change in glibc, keeping a compat symbol under the old name, copying
the test to test the new name and changing the old test to test the
compat symbol.  Jakub has done the corresponding change to the
built-in function in GCC.

Tested for x86_64 and x86.

Add the C23 memalignment function (query the alignment of a pointer)
to glibc.

Given how simple this operation is, it would make sense for compilers
to inline calls to this function, but I'm treating that as a compiler
matter (compilers should add it as a built-in function) rather than
adding an inline version to glibc headers (although such an inline
version would be reasonable as well).  I've filed
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122117 for this feature
in GCC.

Tested for x86_64 and x86.

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.

tst-qsort5 was deleted in 709fbd3ec3595f2d1076b4fec09a739327459288.
Therefore remove its redundant libm dependency.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

C2Y adds unsigned versions of the abs functions (see C2Y draft N3467 and
proposal N3349).

Tested for x86_64.

Signed-off-by: Lenard Mollenkopf <glibc@lenardmollenkopf.de>

If the input buffer exceeds the stack auxiliary buffer, qsort will
malloc a temporary one to call mergesort.  Since C++ standard does
allow the callback comparison function to throw [1], the glibc
implementation can potentially leak memory.

The fixes uses a pthread_cleanup_combined_push and
pthread_cleanup_combined_pop, so it can work with and without
exception enables.  The qsort code path that calls malloc now
requires some extra setup and a call to __pthread_cleanup_push
anmd __pthread_cleanup_pop (which should be ok since they just
setup some buffer state).

Checked on x86_64-linux-gnu.

[1] https://timsong-cpp.github.io/cppwp/n4950/alg.c.library#4

Reviewed-by: DJ Delorie <dj@redhat.com>

This helps with statically interposing getenv.

Updates commit 7a61e7f557a97ab597d6fca5e2d1f13f65685c61
("stdlib: Make getenv thread-safe in more cases").

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Add a test for setenv with updated environ.  Verify that BZ #32588 is
fixed.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Florian Weimer <fweimer@redhat.com>