Ignore .debug_types when reading .debug_aranges

Ignore .debug_types when reading .debug_aranges

I noticed that the fission-reread.exp test case can cause a complaint
when run with --target_board=cc-with-debug-names:

warning: Section .debug_aranges in [...]/fission-reread has duplicate debug_info_offset 0x0, ignoring .debug_aranges.

The bug here is that this executable has both .debug_info and
.debug_types, and both have a CU at offset 0x0.  This triggers the
duplicate warning.

Because .debug_types doesn't provide any address ranges, these CUs can
be ignored.  That is, this bug turns out to be another regression from
the info/types merger patch.

This patch fixes the problem by having this loop igore type units.
fission-reread.exp is updated to test for the bug.