[codeview] Make "clang -g" emit codeview by default when targetting MSVC

Summary:
If you're using the Microsoft ABI, chances are that you want PDBs and
codeview debug info. Currently, everyone has to remember to specific
-gcodeview by default, when it would be nice if the standard -g option
did the right thing by default.

Also, do some related cleanup of -cc1 options. When targetting the MS
C++ ABI, we probably shouldn't pass -debugger-tuning=gdb. We were also
passing -gcodeview twice, which is silly.

Reviewers: smeenai, zturner

Subscribers: aprantl, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D54499

llvm-svn: 346907