[ThinLTO] Fix a few more test match issues

Fix a few more bot failures due to r333335:
- don't match path other than file name, since the delimiter is
different for Windows
- The summary IDs in thinlto-function-summary-refgraph.ll may vary
and therefore can't be matched exactly, because the ordering depends
on the iteration order of the index map which is keyed by GUID. The GUID
for private values will depend on the path.

llvm-svn: 333338