[Sparc] Correctly handle call to functions with ReturnsTwice attribute.

In sparc, setjmp stores only the registers %fp, %sp, %i7 and %o7. longjmp restores
the stack, and the callee-saved registers (all local/in registers: %i0-%i7, %l0-%l7)
using the stored %fp and register windows. However, this does not guarantee that the longjmp
will restore the registers, as they were when the setjmp was called. This is because these
registers may be clobbered after returning from setjmp, but before calling longjmp.

This patch prevents the registers %i0-%i5, %l0-l7 to live across the setjmp call using the register mask.  



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190033 91177308-0d34-0410-b5e6-96231b3b80d8