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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> > The recent changes, #81037 and #87866, were (as far as I know) only intended to change what is printed as error messages, when neither is found, to help users correct their setup for the new style layout. But those changes also seem to have unexpected effects in changing e.g. what gets emitted as embedded directive, when the compiler doesn't see either of them at compile time (with e.g. distributed build systems), while they might be available at link time.
> 
> This matches my understanding. I am not aware of the embedded directive? Do you embed a path to a compiler-rt library to the generated object files?

Clang does this, in a number of cases. In the MSVC ecosystem, one usually invokes `link` or `lld-link` directly, instead of using `clang` to drive the link - therefore, in order to pass implicit libraries to link, like asan/profile, directives are embedded into the generated object files, that tells the linker to link in those libraries.

> I think while technically a new clang can use an old compiler-rt file hierarchy, technically it is unsupported: kinda like that a very old libc++ may not be built with a new Clang.

I don't think anybody is arguing that a new clang should use an old compiler-rt install, but it should be able to use a new install with the layout according to `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR` disabled.

> If we avoid hard-coded library names in compiler-generated relocatable files (just called "object files" on Windows?). there should be no distributed build system concern.

We can't avoid this - we already have this situation. See https://github.com/llvm/llvm-project/pull/87866#issuecomment-2072626122 - #87866 changed the output of the embedded directives when building with a distributed build system, where the compiler doesn't have access to inspect the lib directory that is going to be used to link things in the end.

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