[OpenMP] Use stdlib.h instead of non-standard malloc.h

This fixes a number of OpenMP test failures on macOS.

Author: bryanpkc

openmp/runtime/test/worksharing/for/collapse_test.inc

@@ -1,6 +1,6 @@
 #include <omp.h>
-#include <malloc.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <memory.h>
 
 #define LOOP_IV_TYPE0 LOOP_TYPES