[Android] Enable OpenGL ES 3 by default. Add in a modified GLES3/gl3.h header for supporting it.

Externals/GLES3/GLES3/gl3ext.h

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+#ifndef __gl3ext_h_
+#define __gl3ext_h_
+
+/* $Revision: 17809 $ on $Date:: 2012-05-14 08:03:36 -0700 #$ */
+
+/*
+ * This document is licensed under the SGI Free Software B License Version
+ * 2.0. For details, see http://oss.sgi.com/projects/FreeB/ .
+ */
+
+/* OpenGL ES 3 Extensions
+ *
+ * After an OES extension's interactions with OpenGl ES 3.0 have been documented,
+ * its tokens and function definitions should be added to this file in a manner
+ * that does not conflict with gl2ext.h or gl3.h.
+ *
+ * Tokens and function definitions for extensions that have become standard
+ * features in OpenGL ES 3.0 will not be added to this file.
+ *
+ * Applications using OpenGL-ES-2-only extensions should include gl2ext.h
+ */
+
+#endif /* __gl3ext_h_ */
+

Externals/GLES3/GLES3/gl3platform.h

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+#ifndef __gl3platform_h_
+#define __gl3platform_h_
+
+/* $Revision: 18437 $ on $Date:: 2012-07-08 23:31:39 -0700 #$ */
+
+/*
+ * This document is licensed under the SGI Free Software B License Version
+ * 2.0. For details, see http://oss.sgi.com/projects/FreeB/ .
+ */
+
+/* Platform-specific types and definitions for OpenGL ES 3.X  gl3.h
+ *
+ * Adopters may modify khrplatform.h and this file to suit their platform.
+ * You are encouraged to submit all modifications to the Khronos group so that
+ * they can be included in future versions of this file.  Please submit changes
+ * by sending them to the public Khronos Bugzilla (http://khronos.org/bugzilla)
+ * by filing a bug against product "OpenGL-ES" component "Registry".
+ */
+
+#include <KHR/khrplatform.h>
+
+#ifndef GL_APICALL
+#define GL_APICALL  KHRONOS_APICALL
+#endif
+
+#ifndef GL_APIENTRY
+#define GL_APIENTRY KHRONOS_APIENTRY
+#endif
+
+#endif /* __gl3platform_h_ */