Use the COMPILE_LANGUAGE CMake genexp instead of LINKER_LANGUAGE

[mosra]

With this, the Corrade pedantic flags should no longer cause annoying warning when used with targets that mix C and C++.

Unfortunately, in CMake 3.11 and older, if the projects use just C or CXX, the thing will fail with an error that the language is unknown, which makes it useless. Thus gotta wait with this until 3.12 is the minimum supported: https://gitlab.kitware.com/cmake/cmake/-/commit/4f82199befee194aa924fd4dcdb2f4aad1f7dab6