gdb/testsuite: Test for a backtrace through object without debuginfo

Fedora has been carrying this test since back in the Project Archer
days. A change back then caused GDB to stop being able to backtrace when
only some of the object files had debug information. Even though the
changed code never seems to have made its way into the main GDB project,
I think it makes sense to bring the test along to ensure something like
this doesn't pass unnoticed.