gh-113343: Fix error check on mmap(2) (#113342)

Fix error check on mmap(2)

It should check MAP_FAILED instead of NULL for error.

On mmap(2) man page:

  RETURN VALUE
       On success, mmap() returns a pointer to the mapped area.
       On error, the value MAP_FAILED (that is, (void *) -1) is
       returned, and errno is set to indicate the error.

Python/perf_trampoline.c

@@ -247,7 +247,7 @@ new_code_arena(void)
              mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,
              -1,  // fd (not used here)
              0);  // offset (not used here)
-    if (!memory) {
+    if (memory == MAP_FAILED) {
         PyErr_SetFromErrno(PyExc_OSError);
         PyErr_FormatUnraisable("Failed to create new mmap for perf trampoline");
         perf_status = PERF_STATUS_FAILED;