Implement variadic-def statepoint lowering.
Assign N base/derived non-constant pointers to VRegs, pass others
on stack slots, as in old implementation.
So new statepoint looks like this:
reloc1,reloc2,... = STATEPOINT ..., base1, derived1<tied-def0>, base2, derived2<tied-def1>, ...
N is limited by the maximal number of tied registers machine
instruction can have (15 at the moment).
If any of gc.relocates are not in the same basic block (as the case for
invoke statepoint), use old spilling scheme too.
Full change set is available at D81603.
This line looks unnecessary provided the defs list is marked variadic. If you want to leave it for the moment, that's fine, but I think we can clean this up in a follow up change.
(To be specific, OutOperandList in Target.td for STATEPOINT can be variable_ops, and this line disappears.)