[clang] [llvm] [Driver] Add option to select compiler-rt arch suffix (PR #89775)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I want to hear about opinions why the old compiler-rt file hierarchy is preferred by some users.

Ideally, all operating systems would eventually migrate to `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=on` and adopt a consistent hierarchy similar to libc++/libc++abi/libunwind (without the -arch suffix),
work better with `llvm/runtimes/CMakeLists.txt`, and there will be one less target difference.

For `libc++.so`, once you ship one executable linked against `libc++.so`, you need to keep the filename for compatibility.
However, the OSes (PlayStation and Windows) this patch affects use StaticRuntime and presumably no such compatibility concern.

While some level of fragmentation is acceptable, I hope these exceptions remain the minority.
We already have Windows users with `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=on` (e.g. @tru), so introducing special cases for Windows seems unnecessary.
I am fine with PlayStation being an exception.

If possible, I hope that we avoid a driver option.


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