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/regex/regerror.c

@@ -26,7 +26,7 @@ static const char messages[] = {
   "\0Unknown error"
 };
 
-size_t regerror(int e, const regex_t *preg, char *buf, size_t size)
+size_t regerror(int e, const regex_t *restrict preg, char *restrict buf, size_t size)
 {
 	const char *s;
 	for (s=messages; e && *s; e--, s+=strlen(s)+1);