Revert "try_compile: Honor CMAKE_<LANG>_FLAGS_<CONFIG> changes"

Revert commit v3.6.0-rc1~160^2 (try_compile: Honor
CMAKE_<LANG>_FLAGS_<CONFIG> changes, 2016-04-11).  The behavior it
introduced can break projects that depend on the lack of such behavior.
We will have to introduce a policy or other mechanism to enable the
behavior in a compatible way.  Simply revert it for now.

See issue #16174.