FindProtobuf: improve handling of debug/release libraries on Windows.

It wasn't working if only the debug library was available.
Now I'm using the select_library_configurations macro which handles
all cases properly.
Don't use GLM_FORCE_CXX11.

It makes GLM use C++11 features even when the compiler doesn't support
them. Without that flag, GLM properly checks for available compiler
features before using them.