Fix gles3jni build with clang at android-11

jni/gl3stub.c:21:5: error: implicit declaration of function 'eglGetProcAddress' is invalid in C99
    FIND_PROC(glReadBuffer);
    ^
jni/gl3stub.c:20:37: note: expanded from macro 'FIND_PROC'
    #define FIND_PROC(s) s = (void*)eglGetProcAddress(#s)
                                    ^
1 error generated.

Change-Id: I907f33e3d88f3e96bf7958102e90bf15529748b9

ndk/platforms/android-18/samples/gles3jni/jni/gl3stub.c

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <EGL/egl.h>
 #include "gl3stub.h"
 
 GLboolean gl3stubInit() {