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/stpcpy.c

@@ -9,7 +9,7 @@
 #define HIGHS (ONES * (UCHAR_MAX/2+1))
 #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
 
-char *__stpcpy(char *d, const char *s)
+char *__stpcpy(char *restrict d, const char *restrict s)
 {
 	size_t *wd;
 	const size_t *ws;