- check for arc4random. To make rand.c use it accordingly.
- check for fcntl
- fix fseek detection
- add SIZEOF_CURL_SOCKET_T
- fix USE_UNIX_SOCKETS
- define HAVE_SNPRINTF to 1
- check for fnmatch
- check for sched_yield
- remove HAVE_GETPPID duplicate from curl_config.h
- add HAVE_SENDMSG

Ref: #11964

Co-authored-by: Viktor Szakats
Closes #11973

Follow-up to 9b517c8 curl#11973
Follow-up to 23af112 curl#8680

On Windows this function is exported from winpthread, but winpthread
is never used in Windows builds by curl itself.

In cmake it was marked as never available, but autotools did check
for this function. It found it sometimes (presumable when a dependency
linked to pthread), resulting in a different `curl_config.h`.

Sync the build systems by skipping this check in both, for Windows.

Follow-up to 9b517c8 curl#11973
Follow-up to 23af112 curl#8680

On Windows a successful `sched_yield()` detection requires mingw-w64
built with POSIX threads (not Win32 threads) and GCC (not llvm/clang).
(linking to `winpthread` via custom options may also work.)

In CMake builds, it was pre-cached as unavailable before this patch.

When detected (via autotools), it got only used for Windows XP or older
targets combined with a non-GCC, non-clang compiler that doesn't support
`__builtin_ia32_pause()`, or with the Intel C compiler. According to
`lib/easy_lock.h`.

mingw-w64 only supports GCC and clang, leaving a very narrow chance when
`shed_yield()` gets called on Windows. Even then, `sched_yield()` is
implemented in `winpthread` as `Sleep(0)`, which may or not be a useful.
It's also trivial to implement locally if it is, and such rare build
combination is also deemed useful.

Thus, this patch marks `sched_yields()` permanently unavailable on the
Windows platform also with autotools, and instead of pre-caching, skip
this feature check with CMake.

This syncs `HAVE_SCHED_YIELDS` between builds methods on Windows.

Follow-up to 9b517c8 #11973
Follow-up to 23af112 #8680

Closes #16037

On Windows a successful `sched_yield()` detection requires mingw-w64
built with POSIX threads (not Win32 threads) and GCC (not llvm/clang).
(linking to `winpthread` via custom options may also work.)

In CMake builds, it was pre-cached as unavailable before this patch.

When detected (via autotools), it got only used for Windows XP or older
targets combined with a non-GCC, non-clang compiler that doesn't support
`__builtin_ia32_pause()`, or with the Intel C compiler. According to
`lib/easy_lock.h`.

mingw-w64 only supports GCC and clang, leaving a very narrow chance when
`shed_yield()` gets called on Windows. Even then, `sched_yield()` is
implemented in `winpthread` as `Sleep(0)`, which may or not be a useful.
It's also trivial to implement locally if it is, and such rare build
combination is also deemed useful.

Thus, this patch marks `sched_yields()` permanently unavailable on the
Windows platform also with autotools, and instead of pre-caching, skip
this feature check with CMake.

This syncs `HAVE_SCHED_YIELDS` between builds methods on Windows.

Follow-up to 9b517c8 curl#11973
Follow-up to 23af112 curl#8680

Closes curl#16037