There is a FIXME to add other directories to LLVM_LIBRARY_DIRS. If we don't do that, however, it is the same as LLVM_LIBRARY_DIR. This is sort of a "plan B" revision in case we don't do that FIXME.
I still defined LLVM_LIBRARY_DIRS for sake of downstream projects, but
added a comment saying it was deprecated and should be removed. Is that