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/vdprintf.c

@@ -5,7 +5,7 @@ static size_t wrap_write(FILE *f, const unsigned char *buf, size_t len)
 	return __stdio_write(f, buf, len);
 }
 
-int vdprintf(int fd, const char *fmt, va_list ap)
+int vdprintf(int fd, const char *restrict fmt, va_list ap)
 {
 	FILE f = {
 		.fd = fd, .lbf = EOF, .write = wrap_write,