Patch: Use _Unwind_GetIPInfo in stacktrace.cc

[Andrew Pinski]

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> The new _Unwind_GetIPInfo function allows us to determine if a frame's 
> IP points to the instruction following a call instruction, or to a 
> faulting instruction itself. In the case where it points to a following 
> instruction, we need to "roll back" the IP used in line-number lookup so 
> that the line number is that of the call itself, not the next line.
> 
> Previously we would do this roll-back unconditionally, but this meant 
> that exceptions generated by faults (eg NullPointerException) would 
> sometimes show the wrong line number on their inner-most frame. Using 
> _Unwind_GetIpInfo fixes this.
> 
> I'm also checking in a test case which verifies that stack trace line 
> numbers are correct (now that it finally passes!). I'm checking this in 
> to trunk.

Can you also add a check in configure if _Unwind_GetIPInfo exists?
See PR 26792 for why you need this (there is even a patch against libstdc++
for this configure test).

-- Pinski