lld/lib/Core/Error.cpp: Appease g++-4.7, corresponding to LLVM r210687.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@220039 91177308-0d34-0410-b5e6-96231b3b80d8
[CMake] check-lld: Prune llvm-mc. It is unused.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@220040 91177308-0d34-0410-b5e6-96231b3b80d8