Re-commit: r366610 and r366612: Expand pseudo-components before embedding in llvm-config

There were two main problems:
* The 'nativecodegen' pseudo-component was unconditionally adding
  ${native_tgt}CodeGen even though it conditionally added ${native_tgt}Info and
  ${native_tgt}Desc. This has been fixed by making ${native_tgt}CodeGen
  conditional too
* The 'all' pseudo-component was causing library names like LLVMLLVMDemangle as
  the expansion was to a library name and not a component. There doesn't seem to
  be a list of available components anywhere so this has been fixed by moving the
  expansion of 'all' back where it was before. This manifested in different ways
  on different builders but it was the same root cause

llvm-svn: 366622