fix mingw32/mingw64 build: use system libs and includes rather than prebuilt ones.

CMakeLists.txt

@@ -153,7 +153,7 @@ include_directories(
   ${CMAKE_CURRENT_SOURCE_DIR}/external/xxhash
 )
 
-if(WIN32)
+if(WIN32 AND NOT MINGW)
   include_directories(
     ${CMAKE_CURRENT_SOURCE_DIR}/external/${PLATFORM_FOLDER}-specific/gles/include/OGLES
     ${CMAKE_CURRENT_SOURCE_DIR}/external/${PLATFORM_FOLDER}-specific/icon/include

tests/cpp-empty-test/CMakeLists.txt

@@ -73,3 +73,7 @@ else()
 endif()
 
 target_link_libraries(${APP_NAME} audio cocos2d)
+# MinGW builds need to link libws2_32 and libglew32 manually
+if (MINGW)
+  target_link_libraries(${APP_NAME} glew32 ws2_32)
+endif()

tests/cpp-tests/CMakeLists.txt

@@ -205,6 +205,10 @@ target_link_libraries(${APP_NAME}
   cocos2d
   box2d
 )
+# MinGW builds need to link libws2_32 manually
+if (MINGW)
+  target_link_libraries(${APP_NAME} ws2_32)
+endif()
 
 set(APP_BIN_DIR "${CMAKE_BINARY_DIR}/bin/${APP_NAME}")