fix typo in error string

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@186996 91177308-0d34-0410-b5e6-96231b3b80d8
Add lit magic so that lld unittests are run as part of lld test suite

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187005 91177308-0d34-0410-b5e6-96231b3b80d8