Added pthread.h - necessary on some configurations

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%4019

src/thread/linux/SDL_syssem.c

@@ -54,6 +54,7 @@ static char rcsid =
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>			/* For getpid() */
+#include <pthread.h>
 #include <semaphore.h>
 
 /* Wrapper around POSIX 1003.1b semaphores */