UseCorrade.cmake: more improvements to compatibility mode checker.

Check also that newer unsupported compiler isn't used and fix the
building (the variables were defined after UseCorrade.cmake was
included).
UseCorrade.cmake: check also for compatibility mode for older compilers.

This mode is available only in compatibility branch, but in most cases
UseCorrade.cmake from master is used along it, so it's good to have it
here too.
Sort compiler compatibility modes in descending order.

More users are interested in compatibility with more recent compilers,
so make them first.