[CMake] MingW Update for resource compilation.

[J Decker]

All of the examples indicating ENABLE_LANGUAGE(RC) have the compiler
set afterwards, and it turns out that the following lines work much
better...

I Added these to WIndows-GNU.cmake

SET(CMAKE_RC_COMPILER "windres")
SET(CMAKE_RC_COMPILE_OBJECT "<CMAKE_RC_COMPILER> <FLAGS> <DEFINES> -O
coff -o <OBJECT> <SOURCE>")
ENABLE_LANGUAGE(RC)


by specifying -O coff, it outputs .obj format file containing the
resources, and the link works.

only thing that's really wrong with this is that <FLAGS> is the full
set of C definitions, and it may be different with more or less in
reality.