[clang] [Clang] Add __builtin_bswapg (PR #162433)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> The reason for the failure is that the target platform does not support __int128. If the target platform does not support __int128, perhaps we should skip testing it.
> 
> > > LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `clang` at step 5 "ninja check 1".
> > > Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/24121
> > > Here is the relevant piece of the build log for the reference
> > 
> > 
> > This test failure has been there for over 12 hours at this point. @clingfei and @ojhunt, could one of you either fix the test or revert if you need to investigate?
> 
> I am not sure what you mean by "fix the test", could you please provide a guide?

I've fixed the test locally and just have to turn a build and verify the fix. Not sure why I didn't see the test failure update. I'm just gating the int128 test component on the existence of int128. I'm not sure that the existing tests are really super great here - they're gating on an x86_64 target despite these builtins applying to many archs.

https://github.com/llvm/llvm-project/pull/162433