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/stdio/vfprintf.c

@@ -636,7 +636,7 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
 	return 1;
 }
 
-int vfprintf(FILE *f, const char *fmt, va_list ap)
+int vfprintf(FILE *restrict f, const char *restrict fmt, va_list ap)
 {
 	va_list ap2;
 	int nl_type[NL_ARGMAX+1] = {0};