@beanz tells me it should in fact exists, and it would be bad to put a
list of dirs in LLVM_LIBRARY_DIR. I am therefore making some changes
to help avoid this an other mistakes:
- Use a separate LLVM_CONFIG_LIBRARY_DIR (no "S") variable so we don't start putting a list in LLVM_LIBRARY_DIR by mistake.
- Define the individual dir variables first, and the define the list of dirs variables programmatically.
Also, I rearranged the definitions of the "regular" single dirs below so
LLVM_BINARY_DIR, which is the unsuffixed one, comes first before the