[clang] [clang-driver] don't always set defaultlib=libcmt and defaultlib=oldnames (PR #149400)

[via cfe-commits]

lyj-514328 wrote:

What is the purpose of explicitly adding 'defaultlib' here? When compiling with MSVC header files, the generated object files should already contain the appropriate directives indicating the defaultlib.
Additionally, using the /Bz option with cl.exe also shows that no 'defaultlib' has been added.

https://github.com/llvm/llvm-project/pull/149400