HLSL: allow GS-specific methods in other stages

Using GS methods such as Append() in non-GS stages should be ignored, but was
creating errors due to the lack of a stream output symbol for the non-GS stage.

gtests/Hlsl.FromFile.cpp

@@ -109,6 +109,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.emptystruct.init.vert", "main"},
         {"hlsl.entry-in.frag", "PixelShaderFunction"},
         {"hlsl.entry-out.frag", "PixelShaderFunction"},
+        {"hlsl.fraggeom.frag", "main"},
         {"hlsl.float1.frag", "PixelShaderFunction"},
         {"hlsl.float4.frag", "PixelShaderFunction"},
         {"hlsl.flatten.return.frag", "main"},