feat(libc): implement strsep

[AchrafReyani]

What

Exports strsep with FreeBSD's semantics (lib/libc/string/strsep.c):

• It returns the token at *stringp, ending at the first delimiter.
• The delimiter is overwritten with NUL, and *stringp advances past it.
• Empty fields are returned, unlike strtok.
• When no delimiter is left, *stringp becomes NULL; with *stringp == NULL it returns NULL.

Title: PPSA99169 RetroArch imports it from libSceLibcInternal (resolved through libc.prx), per the #1578 audit. I haven't run the title.

Tested

Windows 11, WinLibs GCC 15.2.0 r7, Release, -DBUILD_TESTING=ON:

• New checks in guest_string_tests, next to the strtok cases:
  • a leading empty field and an empty middle field (",a,,b;c" with ",;");
  • the cursor after each call and NULL after the last token;
  • NULL once exhausted;
  • an empty delimiter set returns the whole string;
  • an empty string returns "" and then NULL.
• Mutation check: delegating to strtok_r, which skips empty fields, makes guest_strings fail.
• cmake --build build --target libs: the patched libc.prx exports cJWGxiQPmDQ.
• tools/check_conventions.py passes, and tools/pr_overlap.py --branch reports no overlap. The function is placed away from the lines feat(libc): implement stpcpy #1812, feat(libc): implement __inet_aton #1848 and feat(libc): implement __inet_addr #1972 change.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• AI-assisted: yes

🤖 Generated with Claude Code

[github-actions]

Progress report (d70b899 → 804674f)

📈 System libraries: 84.7% (+0.01%, +1 implemented functions)

✅ 1 implemented

Library	Name
libc	strsep_nid_postfix

[AchrafReyani]

Full Linux and Windows builds and tests for this head (804674f2), using the project's Build workflow. I can't start the upstream manual run, so I ran the same build.yml in my fork through a mirror PR. Like the upstream run, the jobs check out the PR head merged into current main (d70b8998):

Job	Result
linux	success; full build, ctest: 516/516 passed
windows	success; full build, ctest: 507/507 passed
relinker (Linux, Windows, macOS)	success

Run: https://github.com/AchrafReyani/AnyPS5/actions/runs/37921802565

[oneandonlydean]

Same as #2167, for strsep.

[babyhuey]

@AchrafReyani strsep is now a title's next stop on main. With execvp (#2827) merged, VLC (PPSA85300) on main 06da117 reports this on Linux (catalog build, sce_module/libc.prx unwrapped as #2605 requires):

app.elf: symbol lookup error: app.elf: undefined symbol: cJWGxiQPmDQ

This head (804674f) merges cleanly onto 06da117, guest_strings passes 5/5 (--repeat until-fail:5), and VLC then stops at nanf (DZU+K1wozGI).

[AchrafReyani]

Thanks @babyhuey, resubmitted as #3192, rebased onto current main with your stop.