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/string/strtok.c

@@ -1,6 +1,6 @@
 #include <string.h>
 
-char *strtok(char *s, const char *sep)
+char *strtok(char *restrict s, const char *restrict sep)
 {
 	static char *p;
 	if (!s && !(s = p)) return NULL;