libdw: Handle dwz multi files correctly in dwarf_getfuncs.

Don't use DIE offsets, but use their addresses to make sure they are unique.
Include test cases where main and alt file have subprograms at same offsets.

Reported-by: Josh Stone <jistone@redhat.com>
Signed-off-by: Mark Wielaard <mjw@redhat.com>
7 files changed