Patch: Use _Unwind_GetIPInfo in stacktrace.cc

[Bryce McKinlay]

Andrew Pinski wrote:
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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).

Yes, if libstdc++ introduces a configure test, then I'll use it in 
libjava too. Hopefully it can be put in the common aclocal.m4?

Bryce