Fix pxf unittest compilation
The compilation failed on OSX/clag with the error "implicit declaration of
function 'MemoryContextInit' is invalid".
#include <setjmp.h>
#include "cmockery.h"
-#include "c.h"
+
+#include "postgres.h"
+#include "utils/memutils.h"
/* Define UNIT_TESTING so that the extension can skip declaring PG_MODULE_MAGIC */
#define UNIT_TESTING
