libbacktraceoffline: choose correct debug section for a given address.

1. In /system/lib/libart.so, the ranges of functions covered by .eh_frame
and .ARM.exidx overlap with each other. Currently, we don't check .eh_frame
if the address is in the ranges of functions covered by .ARM.exidx. It leads
to a wrong unwinding result. So change the logic to first try .eh_frame and
.debug_frame, if it fails, then try .ARM.exidx.
2. Add test for Item 1.

Bug: http://b/35251937
Test: run backtrace_test.

Change-Id: Ic412705617c300bc69b4ece178cc2e1bb3eb765b