Slightly better diagnostics on duplicate symbols.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171528 91177308-0d34-0410-b5e6-96231b3b80d8
[Driver] Error on undefined.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171529 91177308-0d34-0410-b5e6-96231b3b80d8
[Passes][GOT] Fix style.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171530 91177308-0d34-0410-b5e6-96231b3b80d8
Style fixes.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171531 91177308-0d34-0410-b5e6-96231b3b80d8