[pdb] Check the display name for <unnamed-tag>, not the linkage name

This issue was encountered on libcmt.pdb, which has a type record that
looks like this:

  Struct (0x1094) {
    TypeLeafKind: LF_STRUCTURE (0x1505)
    MemberCount: 3
    Properties [ (0x200)
      HasUniqueName (0x200)
    ]
    FieldList: <field list> (0x1093)
    DerivedFrom: 0x0
    VShape: 0x0
    SizeOf: 4
    Name: <unnamed-tag>
    LinkageName: .?AU<unnamed-tag>@@
  }

The checks for startswith/endswith "<unnamed-tag>" should look at the
display name, not the linkage name.

llvm-svn: 274376