In r205566, I made a change to Resolver so that Resolver revisit
only archive files in --start-group and --end-group pair. That's
not correct, as it also has to revisit DSO files.
This patch is to fix the issue. I once tried to just revisit DSO
files in a group, but it made Resolver to fall in an infinite loop.
I needed to fix the bug that Resolver loops over a group even if
no undefined symbols are newly created in the group.
Added a test to demonstrate the fix. I confirmed that it succeeded
before r205566, failed after r205566, and is ok with this patch.