-fms-compatibility: Only form implicit member exprs for unqualified ids

If there are any scope specifiers, then a base class must be named or
the symbol isn't from a base class.

Fixes PR19233.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204753 91177308-0d34-0410-b5e6-96231b3b80d8
Use an option alias to implement -gmlt

Review feedback from Reid Kleckner on r203603.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204755 91177308-0d34-0410-b5e6-96231b3b80d8