[compiler-rt] Handle non-canonical triples with new runtime lib layout

As described in Issue #54196
<https://github.com/llvm/llvm-project/issues/54196>, the ideas of `clang`
and `compiler-rt` where runtime libs are located with
`-DLLVM_ENABLE_RUNTIMES` can differ.  This is the `compiler-rt` side of the
patch I've used to get them in sync for the `amd64-pc-solaris2.11` and
`sparc64-unknown-linux-gnu` release builds.

Tested on  `amd64-pc-solaris2.11` and `sparc64-unknown-linux-gnu`.

Differential Revision: https://reviews.llvm.org/D133406