HLSL: Accept SV_Cull/ClipDistanceN, by refactoring the way semantics are mapped.

Test/hlsl.semantic.geom

@@ -0,0 +1,15 @@
+struct S {
+    float clip0 : SV_ClipDistance0;
+    float cull0 : SV_CullDistance0;
+    uint vpai   : SV_ViewportArrayIndex;
+    uint rtai   : SV_RenderTargetArrayIndex;
+    int ii      : SV_InstanceID;
+};
+
+[maxvertexcount(4)]
+S main(triangle in uint VertexID[3] : VertexID,
+       inout LineStream<S> OutputStream)
+{
+    S s;
+    return s;
+}