Features: Make feature recording conditions more consistent

Condition all calls to `_record_compiler_features_{c,cxx}` on
`_result EQUAL 0` so that adding new language standards later does
not need to update them.  Avoid some duplicate compiler version
checks by conditioning C11 and CXX14 feature recording on the
existence of `CMAKE_{C11,CXX14}_STANDARD_COMPILE_OPTION` (whose
setting already used the version check).