[PECOFF] Do not skip COMDAT section symbols.

LLD skipped COMDAT section symbols when reading them because
I thought we don't want to have symbols with the same name.
But they are actually needed because relocations may refer to
the section symbols. So we shoulnd't skip them.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@221329 91177308-0d34-0410-b5e6-96231b3b80d8