Add -gcodeview and -gdwarf to control which type Clang emits

Summary:
By default, 'clang' emits dwarf and 'clang-cl' emits codeview.  You can
force emission of one or both by passing -gcodeview and -gdwarf to
either driver.

Reviewers: dblaikie, hans

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D11742

llvm-svn: 244097