Resolve messy situation with uintptr_t and stdint.h

Platforms common in nixpkgs will have stdint.h - thereby we avoid problems
that seem complicated to avoid.  References:
https://gitlab.com/cmocka/cmocka/-/issues/38#note_1286565655
https://git.alpinelinux.org/aports/plain/main/cmocka/musl_uintptr.patch?id=6a15dd0d0ba9cc354a621fb359ca5e315ff2eabd

It isn't easy, as 1.1.6 codebase is missing stdint.h includes on many places,
and HAVE_UINTPTR_T from cmake also wouldn't get on all places it needs to.
--- a/include/cmocka.h
+++ b/include/cmocka.h
@@ -18,2 +18,4 @@
 #define CMOCKA_H_
+#include <stdint.h>
+#define HAVE_UINTPTR_T 1