SPV: Add SPIRV-Tools validator. This needs the latest SPIR-Tools.

Test/baseResults/hlsl.gatherRGBA.offset.dx10.frag.out

@@ -1261,6 +1261,10 @@ using depth_any
 0:?     '@entryPointOutput.Depth' ( out float FragDepth)
 0:?     '@entryPointOutput.Color' (layout( location=0) out 4-component vector of float)
 
+error: SPIRV-Tools Validation Errors
+error: Expected Image Operand ConstOffsets to be a const object
+  %90 = OpImageGather %v4float %76 %78 %int_0 ConstOffsets %89
+
 // Module Version 10000
 // Generated by (magic number): 80007
 // Id's are bound by 399