Add tests that backtrace and backtrace_symbols produce correct results

[Joseph S. Myers]

On Sun, 20 Jan 2013, Andreas Schwab wrote:

> "Joseph S. Myers" <joseph@codesourcery.com> writes:
> 
> > I'd expect there to be unwind information for read as it's a cancellation 
> > point; the tests themselves are explicitly built with unwind information.  
> 
> This is not a multithreaded program, and read is invisible because it
> does not create a frame in that case.

There must surely be a call frame, where the instructions executed include 
a syscall instruction and a subsequent return, and the return address is 
in the caller of read, and the address of the instruction interrupted by 
the signal should be within read.

For many architectures it's been considered generally useful to annotate 
all .S sources, including syscalls, with unwind information whether or not 
cancellation may occur there.  But if it's not considered desirable to 
have unwind information for all syscalls on some architecture for whatever 
reason, then making the testcase multithreaded would seem a reasonable 
workaround, if it does work.

-- 
Joseph S. Myers
joseph@codesourcery.com