Fix for #7289, add CMake option to enable building with Qt jom (nmake) on Windows

- Can now compile using NMake with jom directly from QtCreator using MSVC compiler (2008) and OSGeo4W devel libs
- Make app capable of running from build directory
- Caveat: may be better way to do it; could have better warning control
Revert unnecessary disabling of unknown warnings
Merge pull request #464 from dakcarto/nmake-with-jom_1

Fix for #7289, add CMake option to enable building with Qt jom (nmake) on Windows