Summary:
1. Find GCC's LDPATH from the actual GCC config file.
2. Avoid picking libraries from a similar named tuple if the exact
tuple is installed.
Reviewers: mgorny, chandlerc, thakis, rnk
Reviewed By: mgorny, rnk
Subscribers: cfe-commits, mgorny
Differential Revision: https://reviews.llvm.org/D45233
llvm-svn: 329512