[llvm] [GlobalISel] Add G_ADD for computeNumSignBits (PR #159202)

[Yatao Wang via llvm-commits]

ningxinr wrote:

> LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/31422
> 
> Here is the relevant piece of the build log for the reference

This one looks like an irrelevant intermittent failure. It timed out, similar to another failure that happened a day ago: https://lab.llvm.org/buildbot/#/builders/129/builds/31372

https://github.com/llvm/llvm-project/pull/159202