libdwfl: Allow partial relocations also for debug files.

libdwfl: Allow partial relocations also for debug files.

__libdwfl_relocate is called for get_dwarf and get_elf. We allow not all
relocations to be resolved for Elf files, but required all relocations
(in the debug sections) to be fully resoled in Dwarf files. This used to
mostly work out with .o ET_REL files when the main Elf was gotten before
the Dwarf. But with .dwo files, we (readelf) might open the .o file just
for the (skeleton) Dwarf. In this case it could happen not all relocations
in the debug sections could be resolved (.debug_info and .debug_addr might
contain referenes to undefined symbols). So allow partial relocations
also for debug files.

Signed-off-by: Mark Wielaard <mark@klomp.org>