build: Check for EGL support in libepoxy on Windows

build: Check for EGL support in libepoxy on Windows

...EGL support needs to be explicitly enabled during the build of
libepoxy on Windows as it is not enabled by default on Windows.

With this, we can add an EGL renderer for Windows that make use of
Google's libANGLE, which is a library that translates OpenGL/ES calls
to Direct3D 9/11, which will provide better hardware compatibility
on Windows and would act as one of the foundations to resolve issue #105.