[clang] [Driver] Normalize the baremetal handling of libc++ and runtimes (PR #101259)

[Peter Smith via cfe-commits]

https://github.com/smithp35 approved this pull request.

LGTM too, I've checked that the `-DLIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY=ON` works. We, and other bare-metal driver using toolchains can adopt that.

https://github.com/llvm/llvm-project/pull/101259