[extrowerk]

Add the <stdlib.h> interfaces that were not bound for illumos yet:
clearenv, closefrom, fdwalk, canonicalize_file_name, rand_r,
the *rand48 family and random/srandom/initstate/setstate,
plus basename and dirname from <libgen.h>. These all carry
SUNW_* symbol versions and go in the shared solarish module.

The newer OpenBSD/POSIX 2024 compatibility functions (mkostemp,
mkostemps, qsort_r, reallocarray, reallocf, recallocarray,
freezero, strtonum) are illumos-only (ILLUMOS_* versions) and go in
the illumos module. illumos' qsort_r uses the POSIX argument order.

libgen.h is added to the solarish ctest headers.

stdlib.h: https://github.com/illumos/illumos-gate/blob/b56614870515295c253babb2b10fffdd3c60fdbe/usr/src/head/stdlib.h#L145-L161
stdlib.h: https://github.com/illumos/illumos-gate/blob/b56614870515295c253babb2b10fffdd3c60fdbe/usr/src/head/stdlib.h#L208-L248
stdlib.h: https://github.com/illumos/illumos-gate/blob/b56614870515295c253babb2b10fffdd3c60fdbe/usr/src/head/stdlib.h#L276-L359
libgen.h: https://github.com/illumos/illumos-gate/blob/b56614870515295c253babb2b10fffdd3c60fdbe/usr/src/head/libgen.h#L52-L53
Symbol versions: https://github.com/illumos/illumos-gate/blob/b56614870515295c253babb2b10fffdd3c60fdbe/usr/src/lib/libc/port/mapfile-vers

Testing

• cargo check for x86_64-unknown-illumos, aarch64-unknown-illumos,
  x86_64-pc-solaris and sparcv9-sun-solaris (with -Dwarnings).
• Every name in the applicable libc-test/semver lists compiles for
  illumos and Solaris; new constant values were cross-checked
  mechanically against the illumos-gate headers.
• ci/style.py checks (rustfmt, sorted/unique semver lists, style test).
• CC=clang cargo test -p libc-test on OmniOS r151060 (x86_64): passes

@rustbot label stable-nominated

🤖 Generated with Claude Code

https://claude.ai/code/session_01PUjq5rfL3s7TbKS3PeAE5K

[rustbot]

Some changes occurred in a solarish module

cc @jclulow, @pfmooney

[tgross35]

Rewrite commit messages and PR descriptions by hand, then you may unmark as a draft. See https://forge.rust-lang.org/policies/llm-usage.html#-banned.