LibC: Add definitions for INTMAX_C and UINTMAX_C

Userland/Libraries/LibC/bits/stdint.h

@@ -138,6 +138,9 @@ typedef __INTMAX_TYPE__ intmax_t;
 #define INT64_C(x) x##LL
 #define UINT64_C(x) x##ULL
 
+#define INTMAX_C(c) c##LL
+#define UINTMAX_C(c) c##ULL
+
 #define SIZE_MAX ((size_t)-1)
 
 __END_DECLS