Try to resolve symbol differences early, and if successful create a plain

Try to resolve symbol differences early, and if successful create a plain
data fragment. This reduces the time to assemble the test in 8711 from 60s to
54s.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120767 91177308-0d34-0410-b5e6-96231b3b80d8