[clang] [Driver] Restore compiler-rt arch suffix for PS and Windows (PR #89775)

[Fangrui Song via cfe-commits]

MaskRay wrote:

I understand that there is some distributed build system pain and I feel sympathy.
However, I have pointed out that it is *unsupported* to not provide files for driver probing, therefore I am not sure it is fair to revert the patches improving
`LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=on` users.

Again, clangDriver does file probing in various places. If you want a specific driver decision, provide sufficient files to make it make the best guess for you.

If `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=off` users are willing to accept less test coverage, we can swap the probed paths in `ToolChain::getCompilerRT` if `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=off`.

I am also fine if Windows users decide to prefer UI for `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=off` configurations and add a `isOSWindows()` check somewhere.


https://github.com/llvm/llvm-project/pull/89775