Make clang-cl accept .lib inputs (PR20065)

Patch by Ehsan Akhgari!

(Tiny tweak by me: renamed PathSegment to LibDir.)

Differential Revision: http://reviews.llvm.org/D4192

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211189 91177308-0d34-0410-b5e6-96231b3b80d8