workaround for error building with clang and quiet some warnings building without libmv.

intern/guardedalloc/MEM_sys_types.h

@@ -94,7 +94,9 @@ typedef unsigned long uintptr_t;
 #include <stdint.h>
 
 /* XXX */
-#ifndef uint64_t
+
+#ifndef UINT64_MAX
+# define UINT64_MAX		18446744073709551615
 typedef uint8_t   u_int8_t;
 typedef uint16_t  u_int16_t;
 typedef uint32_t  u_int32_t;