[ThinLTO] Update test to be more tolerant of ordering changes

[ThinLTO] Update test to be more tolerant of ordering changes

Update the ThinLTO function importing test to use DAG forms of checks so
that it is more tolerant of changes to relative ordering between
imported decls/defs. This reduces the number of changes required by the
comdat importing patch I am sending for review shortly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252932 91177308-0d34-0410-b5e6-96231b3b80d8