[llvm] [RISCV] Make XFAIL test UNSUPPORTED. (PR #168525)

[Craig Topper via llvm-commits]

topperc wrote:

> > > Approving so this can fix the bots.
> > > I presume the issue is some bots have asserts enabled and some don't
> > 
> > 
> > @lenary oh, right. I guess the proper fix would have been to add "requires asserts".
> 
> This is probably the correct fix. I also saw this test failure on my bot that specifically builds without asserts: https://lab.llvm.org/buildbot/#/builders/202/builds/4233

The correct fix is to change the `llvm_unreachable` to a `reportFatalError`. If there is an input that can reach an `llvm_unreachable`, then it is not "unreachable"

https://github.com/llvm/llvm-project/pull/168525