cmake HAVE_XAUDIO2_H examples

nvMcJohn/apitest thirdparty/SDL2-2.0.1/CMakeLists.txt :762 

check_include_file(xaudio2.h HAVE_XAUDIO2_H)

nvMcJohn/apitest thirdparty/SDL2-2.0.1/CMakeLists.txt :788 

endif(HAVE_XAUDIO2_H)