[clang] [clang][Driver][BareMetal] Support --cstdlib in clang-runtimes sysroot lookup (PR #185870)

[Volodymyr Turanskyy via cfe-commits]

voltur01 wrote:

As discussed in the last Embedded WG sync up (https://discourse.llvm.org/t/llvm-embedded-toolchains-working-group-sync-up/63270/94), I am closing this PR and creating a new one to pass `--cstdlib` to multilibs to handle it there: https://github.com/llvm/llvm-project/pull/203884

https://github.com/llvm/llvm-project/pull/185870