[flang] [clang] [flang][windows] Add option to link against specific MSVC CRT (PR #70833)

[David Truby via cfe-commits]

DavidTruby wrote:

I've also started the work to get linker option directives (like "/DEFAULTLIB") added to MLIR's LLVMIR dialect so that we can do this the correct way: see #71720. I'd still like to merge this patch first though for the incremental improvement it does provide. Then once the MLIR support is merged I can switch over to using that and this should be resolved in the way that would help CMake's support for flang. 

https://github.com/llvm/llvm-project/pull/70833