Introduce tests/prof_cmocka.h

As 9f2abc75 accidentally got the ordering of some of the includes wrong,
I decided to propose my initial solution again.

Additional to that, I've opened a MR against CMocka to solve this on
their side, since I believe that the current way this is done is not
sustainable [0].

[0] https://gitlab.com/cmocka/cmocka/-/merge_requests/91

Fixes: 9f2abc75 ("Fix tests with gcc15 (uintptr_t)")
Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

CProof note: our new tests need to also be updated.

tests/functionaltests/proftest.c

@@ -2,11 +2,8 @@
 #include <sys/wait.h>
 #include <glib.h>
 
-#include <setjmp.h>
-#include <stdarg.h>
-#include <stddef.h>
 #include <stdlib.h>
-#include <cmocka.h>
+#include "prof_cmocka.h"
 #include <stdio.h>
 #include <unistd.h>
 #include <errno.h>