[Chapel Merge] Fix bundled LLVM builds

Branch: refs/heads/main
Revision: 95c7d7b
Author: mppf
Log Message:

Merge pull request #17979 from mppf/fix-llvm-bundled-17923

Fix bundled LLVM builds

Fixes CHPL_LLVM=bundled builds after PR #17923.

  • Allows the configured CHPL_LLVM_CONFIG to not exist yet for
    CHPL_LLVM=bundled without giving an error
  • Improves the errors from make for a failed printchplenv to be less

Reviewed by @daviditen - thanks!