And share some code with lld-link.
While here, also add a FIXME about PR42180 and merge r360150 to llvm-lib.
Differential Revision: https://reviews.llvm.org/D63021
llvm-svn: 363016
This reorganisation prevents us from cluttering up the top-level lib directory
with more driver libraries such as llvm-dlltool (see D29892).
llvm-svn: 302995