Disable check for pthread_spin_lock() since it doesn't support
PTHREAD_PROCESS_SHARED.  This causes libqb to fallback gracefully
to using pthread mutexes without having to patch anything.

--- configure.ac.orig	2017-12-21 09:02:11 UTC
+++ configure.ac
@@ -218,7 +218,7 @@ AC_CHECK_FUNCS([alarm clock_gettime \
 AX_SAVE_FLAGS
 CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
 LIBS="$LIBS $PTHREAD_LIBS"
-AC_CHECK_FUNCS([pthread_spin_lock pthread_setschedparam \
+AC_CHECK_FUNCS([pthread_setschedparam \
 		pthread_mutexattr_setpshared \
 		pthread_condattr_setpshared \
 		sem_timedwait semtimedop])