modules: updated FindMagnum.cmake.

Affects only WindowlessWglApplication.
modules: updated FindCorrade.cmake and FindMagnum.cmake.
Merge branch '_modules_' into _modules_sdl2_
Merge branch '_modules_sdl2_' into _modules_es2_
Merge branch '_modules_es2_' into base-nacl

Conflicts:
	modules/FindCorrade.cmake