[AsmPrinter] Allow emitting codeview for any windows target

Before SVN r244158, codeview debug info was emitted always
emitted for msvc if debug info was enabled, but that commit
added a module flag.

Since it's still restricted by the flag, we can allow it
for any target if the user requests it, not only msvc (and
windows-itanium, added in SVN r287567).

Add a test for emitting it for a mingw target.

Differential Revision: https://reviews.llvm.org/D46303

llvm-svn: 331809