[Driver] Move LIBRARY_PATH before user inputs

Fixes PR16786

Currently, library paths specified by LIBRARY_PATH are placed after inputs: `inputs LIBRARY_PATH stdlib`
In gcc, the order is: `LIBRARY_PATH inputs stdlib` if not cross compiling.
(On Darwin targets, isCrossCompiling() always returns false.)

This patch changes the behavior to match gcc.

Reviewed By: hfinkel

Differential Revision: https://reviews.llvm.org/D65880

llvm-svn: 368245