Move hwc tests to libc++.

Since these tests were pulling in a static library linked against
stlport, the tests needed to be explicit about which STL they're
using. Might as well be libc++.

Bug: 15193147
Change-Id: I4e0fc4ea10f7982dd04e7baaf57139dd5d55543e
diff --git a/opengl/tests/hwc/hwcTestLib.cpp b/opengl/tests/hwc/hwcTestLib.cpp
index 9b224e2..d5ce448 100644
--- a/opengl/tests/hwc/hwcTestLib.cpp
+++ b/opengl/tests/hwc/hwcTestLib.cpp
@@ -20,17 +20,18 @@
  * Utility library functions for use by the Hardware Composer test cases
  */
 
+#include <arpa/inet.h> // For ntohl() and htonl()
+
+#include <cmath>
 #include <sstream>
 #include <string>
 
-#include <arpa/inet.h> // For ntohl() and htonl()
-
 #include "hwcTestLib.h"
 
 #include "EGLUtils.h"
 
 // Defines
-#define NUMA(a) (sizeof(a) / sizeof(a [0]))
+#define NUMA(a) (sizeof(a) / sizeof((a)[0]))
 
 // Function Prototypes
 static void printGLString(const char *name, GLenum s);