New Issue: "error: This compiler was built without LLVM support" could be clearer

18073, "bradcray", ""error: This compiler was built without LLVM support" could be clearer", "2021-07-16T18:28:21Z"

As an experienced Chapel user, I had some confusion yesterday when I started getting errors of the form:

error: This compiler was built without LLVM support

for anything I tried to do with my install. It turns out that the source of the problem was that I indeed had built my compiler with CHPL_LLVM=none, but that in my current working environment, I had CHPL_LLVM=system set. I understand now that this means that I was requesting a configuration that the compiler doesn't support, but I don't think this will be particularly clear to a typical / novice end-user given how much it gave me pause. Something like:

error: You have requested a 'CHPL_LLVM=system' compilation, but this compiler was built without LLVM support.  Either set `CHPL_LLVM=none` or re-build your compiler with LLVM enabled

(where obviously it would use bundled rather than system if that's what I had set it to.