[Sparc] Implement __builtin_setjmp, __builtin_longjmp back-end.

This code implements builtin_setjmp and builtin_longjmp exception handling intrinsics for 32-bit Sparc back-ends.

The code started as a mash-up of the PowerPC and X86 versions, although there are sufficient differences to both that had to be made for Sparc handling.

Note: I have manual tests running. I'll work on a unit test and add that to the rest of this diff in the next day.

Also, this implementation is only for 32-bit Sparc. I haven't focussed on a 64-bit version, although I have left the code in a prepared state for implementing this, including detecting pointer size and comments indicating where I suspect there may be differences.

Differential Revision: http://reviews.llvm.org/D19798

llvm-svn: 268483