librhash: Avoid incorrect int8_t definition with PGI on Linux ppc64le

`sys/types.h` defines `int8_t` incorrectly as `char` which is unsigned.
Adjust ordering so `inttypes.h` defines it as `signed char` first.

Utilities/cmlibrhash/librhash/rhash.c

@@ -18,6 +18,8 @@
 #define _LARGEFILE64_SOURCE
 #define _FILE_OFFSET_BITS 64
 
+#include "ustd.h"   /* Need this first within CMake.  */
+
 #include <string.h> /* memset() */
 #include <stdlib.h> /* free() */
 #include <stddef.h> /* ptrdiff_t */