docs(libSceLibcInternal): record that the _Mtx helpers follow PS4 code

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/dev/debt/libSceLibcInternal.md

@@ -344,6 +344,7 @@ The named entries below use provider-specific NID aliases to avoid interposing h
 - [_err, _warn](../../../core/libs/prx/libSceLibcInternal/Err.cpp) and [_getprogname](../../../core/libs/prx/libSceLibcInternal/Export.cpp) (libSceLibcInternal) are assumed to be the same functions as `err`, `warn` and `getprogname` and run their code; the console's module was not read. FreeBSD 11.4 defines the underscore names and makes the public names weak references to them ([`_err`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/lib/libc/gen/err.c#L70-L79), [`_warn`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/lib/libc/gen/err.c#L135-L144), [`_getprogname`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/lib/libc/gen/getprogname.c#L10-L17))
 - [inet_aton, inet_addr, inet_ntoa and inet_ntoa_r](../../../core/libs/prx/libSceLibcInternal/Inet.cpp) (libSceLibcInternal) follow the FreeBSD code in the console's `libSceLibcInternal.sprx` (SDK 4.5x build of `J03950001`, 0x8ADE0 to 0x8B3D0) and matched it on a PS5 (firmware 13.60) for 20 `inet_aton` inputs; a null text, which the console dereferences, throws. `inet_ntoa_r` formats through libkernel's `__inet_ntop`, so a null buffer with room for the text throws and a null buffer that is too small sets `ENOSPC`, as `__inet_ntop` does for a null destination; the console's `inet_ntoa_r` was not measured with a null buffer
 - [__inet_ntoa_r](../../../core/libs/prx/libSceLibcInternal/Inet.cpp) (libSceLibcInternal) was not measured on the console: it runs `inet_ntoa_r`, as FreeBSD 11.4 names the function `__inet_ntoa_r` ([arpa/inet.h](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/include/arpa/inet.h#L129)) and makes `inet_ntoa_r` a weak alias of it ([inet_ntoa.c](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/lib/libc/inet/inet_ntoa.c#L62-L76))
+- [_Mtxinit, _Mtxlock, _Mtxunlock, _Mtxdst](../../../core/libs/prx/libSceLibcInternal/Mutex.cpp) (libSceLibcInternal) follow the PS4 code of [shadPS4](https://github.com/shadps4-emu/shadPS4/blob/860d73b7e99559106a3ffa3d3d69f0f9237e115e/src/core/libraries/libc_internal/libc_internal_threads.cpp#L10-L62) and [fpPS4](https://github.com/red-prig/fpPS4/blob/04cefd43e6fddd1ab033e7980cd356d14c964905/src/libcinternal/ps4_mtx_internal.pas#L47-L99): the argument points to a pointer-sized libkernel mutex handle, `_Mtxinit` creates it recursive, a zeroed handle becomes an error-checking mutex on its first lock as with the POSIX calls, and each returns 0 on success and 1 on any failure. A null handle pointer throws in libkernel. The `SceLibcI_` name goes to `scePthreadMutexInit`, which drops it. For PS5 only the names are known (NID hashes, ps5sdk stubs); layout, signatures, mutex type and results are not verified on a PS5
 
 ### Additional PS5 3.20 imports (xdCloudy #9498)