Get rid of all references to soimm in MipsConstantIslands pass because
we don't have such an operand.
Suprisingly enough, this is never actually accounted for in the 
ARM version when determining offset ranges. In both places there is the
comment:
-    // FIXME: Make use full range of soimm values.
(soimm = shift operand immediate).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194101 91177308-0d34-0410-b5e6-96231b3b80d8
Slightly change the way stackmap and patchpoint intrinsics are lowered.

MorphNodeTo is not safe to call during DAG building. It eagerly
deletes dependent DAG nodes which invalidates the NodeMap. We could
expose a safe interface for morphing nodes, but I don't think it's
worth it. Just create a new MachineNode and replaceAllUsesWith.

My understaning of the SD design has been that we want to support
early target opcode selection. That isn't very well supported, but
generally works. It seems reasonable to rely on this feature even if
it isn't widely used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194102 91177308-0d34-0410-b5e6-96231b3b80d8