[Driver] Change MipsLinux default linker from "lld" to "ld.lld"

Reviewers: kzhuravl, atanasyan

Reviewed By: atanasyan

Subscribers: sdardis, arichardson, jrtc27, atanasyan, cfe-commits

Differential Revision: https://reviews.llvm.org/D51234

llvm-svn: 340709