Fix indentation, use early return.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194619 91177308-0d34-0410-b5e6-96231b3b80d8
Show error message if two atoms are not mergeable.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194620 91177308-0d34-0410-b5e6-96231b3b80d8