nptl: do not define _POSIX_SPAWN since its not implemented

Building things like vlc checks if _POSIX_SPAWN is defined. Since
posix_spawn is not implemented we dont define it.

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>

libpthread/nptl/sysdeps/unix/sysv/linux/bits/posix_opt.h

@@ -143,8 +143,10 @@
 /* We support spinlocks.  */
 #define _POSIX_SPIN_LOCKS	200809L
 
+#if 0
 /* The `spawn' function family is supported.  */
 #define _POSIX_SPAWN	200809L
+#endif
 
 /* We have POSIX timers.  */
 #define _POSIX_TIMERS	200809L