third_party/threads: Use PTHREAD_MUTEX_RECURSIVE by default
PTHREAD_MUTEX_RECURSIVE_NP was used for compatibility with old glibc.
Although due to the_GNU_SOURCES define the portable,
PTHREAD_MUTEX_RECURSIVE will be available for Linuxes since at least
1998. Simplify things giving us compatibility with musl which
apparently does not provide the non-portable define.
Inspired by almost identical commit in mesa
aead7fe2e2b(c11/threads: Use
PTHREAD_MUTEX_RECURSIVE by default) by Felix Janda.
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>