libdw: Fix dwarf_peel_type infinite loop.

libdw: Fix dwarf_peel_type infinite loop.

We were calling dwarf_attr_integrate () in the die in the loop instead of
on the result. Which would cause an infinite loop when die != result.
Add a testcase that explicitly checks this case.

https://sourceware.org/bugzilla/show_bug.cgi?id=21330

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