[PATCH] [Sanitizer] Update GetMaxVirtualAddress for PowerPC64 Linux

[Jay Foad]

>>! In D6082#4, @kcc wrote:
> Do we need to support 44-bit AS at all? 
> Why not just support the new ans shiny 46 bit? 

I can't answer that. It's a question for the sanitizer maintainers. Do you want to support PowerPC64 on Linux older than 3.7 (released about two years ago)? Do you support PowerPC64 on any other OSes?

Personally, I'd be very happy with only supporting 46-bit. But I was trying to be conservative, by fixing the modern Linux case but not breaking any other setups that might already have been working.

> If we absolutely need this, maybe try mapping something in a few different places and see if 46 bits work? 

Sure, if you'd prefer that approach, I'll try to come up with a patch.

http://reviews.llvm.org/D6082