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/pthread_attr_setschedparam.c

@@ -1,6 +1,6 @@
 #include "pthread_impl.h"
 
-int pthread_attr_setschedparam(pthread_attr_t *a, const struct sched_param *param)
+int pthread_attr_setschedparam(pthread_attr_t *restrict a, const struct sched_param *restrict param)
 {
 	if (param->sched_priority) return ENOTSUP;
 	return 0;