Force TARGET_GLES on Windows RT.

CMakeLists.txt

@@ -32,8 +32,9 @@ find_package(Corrade REQUIRED)
 
 include(CMakeDependentOption)
 
-# If targeting Android, NaCl or Emscripten, set explicit OpenGL ES support
+# If targeting Android, NaCl, Emscripten or Windows RT, set explicit OpenGL ES
-if(NOT CORRADE_TARGET_ANDROID AND NOT CORRADE_TARGET_EMSCRIPTEN AND NOT CORRADE_TARGET_NACL)
+# support
+if(NOT CORRADE_TARGET_ANDROID AND NOT CORRADE_TARGET_EMSCRIPTEN AND NOT CORRADE_TARGET_NACL AND NOT CORRADE_TARGET_WINDOWS_RT)
     option(TARGET_GLES "Build for OpenGL ES / WebGL" OFF)
 else()
     set(TARGET_GLES ON)