Fix mac build

Macs don't have malloc.h, hopefully this fixes the build.

(cherry picked from commit 6cc5076a1248582cf16bd9a6a1719e0a4c1a1de2)

Change-Id: I94d10d2c3d16893625df210bdd5587eea4a1247f
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index d957d27..a1ac2f0 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -21,11 +21,14 @@
 
 #include <fstream>
 #include <iostream>
-#include <malloc.h>  // For mallinfo
 #include <sstream>
 #include <string>
 #include <vector>
 
+#ifndef __APPLE__
+#include <malloc.h>  // For mallinfo
+#endif
+
 #if defined(__linux__) && defined(__arm__)
 #include <sys/personality.h>
 #include <sys/utsname.h>