[libclc] [llvm] [flang-rt][libclc] Install multilib variants in their own directory (PR #230251)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> libclc change LGTM. Is there a libclc multilib use case, or is this for consistency?

Theoretically, if you wanted to build it with a sanitizer in the future, but the layer is usually pretty thin so I don't know how much it would cover.

https://github.com/llvm/llvm-project/pull/230251