[compiler-rt] [compiler-rt] [test] Fix using toolchains that rely on Clang default configs (PR #113491)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

FWIW, I'm not particularly happy about this solution, but I don't really see any other good alternatives either, between toolchains that have "mostly opinion" default configs and toolchains that have a hard dependency on their config files.

https://github.com/llvm/llvm-project/pull/113491