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/signal/sigprocmask.c

@@ -1,7 +1,7 @@
 #include <signal.h>
 #include <errno.h>
 
-int sigprocmask(int how, const sigset_t *set, sigset_t *old)
+int sigprocmask(int how, const sigset_t *restrict set, sigset_t *restrict old)
 {
 	int r = pthread_sigmask(how, set, old);
 	if (!r) return r;