[codeview] Add .cv_string directive for testing purposes

The main use case for this directive is to allow assembly writers to
write their own FPO data strings without going through the .cv_fpo*
directive family.

I'm experimenting with different RPN programs to fix PR38857, and I
figured I should go ahead and make this directive permanent.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341712 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed