Add support for spirv1.6

Add command line support which enables the following behavior:

- Remap discard

  Map discard to DemoteToHelperInvocation for HLSL shaders. Map to
  OpTerminateInvocation for GLSL shaders.

- Decorate HelperInvocation with Volatile

- Use localSizeId for execution mode

  WorkGroupSize is deprecated in spirv1.6

Also update known goods to SPIRV 1.6

Test/hlsl.spv.1.6.discard.frag

@@ -0,0 +1,14 @@
+void foo(float f)
+{
+	if (f < 1.0)
+		discard;
+}
+
+void PixelShaderFunction(float4 input) : COLOR0
+{
+    foo(input.z);
+	if (input.x)
+		discard;
+	float f = input.x;
+	discard;
+}