Allow intrinsics to be used in place of node matchables.

TableGen has support for using an intrinics name directly in a DAG,
but this breaks down when referring to just a node, as that's
handled initializer list stuff entirely via subclassing in the
parser. That is, using an instrinsic like "(int_my_intrinsic ...)"
works fine. Using it standalone for parameterizing the operator
in such a DAG does not.

Fixing this is simple enough, as we simply declare Intrinsic
as deriving from SDPatternOperator, which is the class name
intended for exactly this purpose in TargetSelectionDAG.td.

When the intrinsic is actually used in the DAG pattern, it will
be recognized and expanded to an intrinsic_wo_chain (et. al.)
just like when it's used directly.

Incoming ARM NEON cleanup based on this and a bit of functionality
improvement after that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159973 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Intrinsics.td

@@ -161,10 +161,11 @@ def llvm_vararg_ty     : LLVMType<isVoid>;   // this means vararg here
 //    intrinsic.
 //  * Properties can be set to describe the behavior of the intrinsic.
 //
+class SDPatternOperator;
 class Intrinsic<list<LLVMType> ret_types,
                 list<LLVMType> param_types = [],
                 list<IntrinsicProperty> properties = [],
-                string name = ""> {
+                string name = ""> : SDPatternOperator {
   string LLVMName = name;
   string TargetPrefix = "";   // Set to a prefix for target-specific intrinsics.
   list<LLVMType> RetTypes = ret_types;