[PATCH] libdwfl: Handle unwind frame when the return address register isn't set.

[Mark Wielaard]

On Tue, 2018-04-10 at 16:23 +0200, Mark Wielaard wrote:
> When we have unwound the frame and then cannot set the return address
> we wouldn't set any error. That meant that a dwfl_thread_getframes ()
> call could end in an error, but without any dwfl_errno set, producing
> the "no error" error message.
> 
> If we cannot set the return address at the end of unwinding the frame
> that means that either the return address register is bogus (error),
> or that the return address is undefined (end of the call stack).
> 
> This fixes the run-backtrace-native-biarch.sh testcase for me on an
> i386 on x86_64 setup with gcc 7.2.1 and glibc 2.17.

Pushed to master.