`compiler-builtins` test no longer passing on `ppc64le`

[nbdd0121]

The current HEAD of compiler-builtin's master branch no longer passes CI tests. Error reports failing at testcrate/tests/cmp.rs:34:9 for powerpc64le-unknown-linux-gnu target.

Bisection shows that the test still builds in nightly-2021-08-21 but fails in nightly-2021-08-22, so I suspect the issue is from LLVM upgrade #87570.

Initially discovered in rust-lang/compiler-builtins#405.

[tgross35]

Any idea if this still a problem? There are a handful of functions in libm that were skipped with a link to this issue, but I have seemingly been able to enable them again.

[Amanieu]

The issues were likely caused by LLVM so if it works now then it most likely has been fixed in the latest LLVM upgrade. If it passes CI then it's fine to just re-enable these.