[design] role of CHPL_TARGET_COMPILER in LLVM compiles

Hi all —

We've currently got a somewhat strange relationship between using C or LLVM as the back-end compiler, the CHPL_TARGET_COMPILER setting and the --llvm flag. Over in this issue, there's a proposal to try to unify things a bit better. Head over, take a look, and comment if this is something you feel invested in or would like to learn more about: