Fix forwarding -l to MSVC's link.exe

Translate -lfoo to -lfoo.lib while making sure that -lfoo.lib stays as
-lfoo.lib. Also, these arguments were being passed twice: once
explicitly via AddAllArgs, and again implicitly as linker inputs. Now
they are passed once.

Fixes PR20868.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@217895 91177308-0d34-0410-b5e6-96231b3b80d8