use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

src/thread/sem_getvalue.c

@@ -1,6 +1,6 @@
 #include <semaphore.h>
 
-int sem_getvalue(sem_t *sem, int *valp)
+int sem_getvalue(sem_t *restrict sem, int *restrict valp)
 {
 	int val = sem->__val[0];
 	*valp = val < 0 ? 0 : val;