[compiler-rt] [compiler-rt][test] Remove noisy warnings (PR #191510)

[Florian Mayer via llvm-commits]

fmayer wrote:

If the warnings point at some real problem, we should keep them even if we don't fix it, for posterity. Or at least keep a comment about the problem in the lit cfg.

https://github.com/llvm/llvm-project/pull/191510