[compiler-rt] [llvm] Reland check-builtins target for LLVM_ENABLE_RUNTIMES (PR #171941)

[Andrew Haberlandt via llvm-commits]

ndrewh wrote:

The last time we landed this there were also issues on the powerpc bots, which appear unrelated. I think I will have to look at how to fix these first.

> LLVM Buildbot has detected a new failure on builder clang-ppc64-aix running on aix-ppc64 while building llvm at step 6 "test-build-unified-tree-check-all".

https://lab.llvm.org/buildbot/#/builders/64/builds/6777

> LLVM Buildbot has detected a new failure on builder clang-ppc64le-rhel running on ppc64le-clang-rhel-test while building llvm at step 6 "test-build-unified-tree-check-all".

https://lab.llvm.org/buildbot/#/builders/145/builds/11398

https://github.com/llvm/llvm-project/pull/171941