Resolve build issue for unittest

deepikabhavnani · deepikabhavnani · commit 2df0289ae90d · 2018-11-26T09:53:19.000-06:00
Error Resolved here is:
SingletonPtr.h:93:13: error: ‘NULL’ was not declared in this scope
diff --git a/platform/SingletonPtr.h b/platform/SingletonPtr.h
@@ -23,6 +23,7 @@
 #ifndef SINGLETONPTR_H
 #define SINGLETONPTR_H
 
+#include <stdlib.h>
 #include <stdint.h>
 #include <new>
 #include "platform/mbed_assert.h"
