Fix ExecutionMode's crashing drivers with compute based mesh output.

The OpExecutionMode entries were being left in place, but pointing
to functions which are no longer entry points.  This caused the GPU
driver to crash (probably trying to look it up).

renderdoc/driver/vulkan/vk_postvs.cpp

@@ -659,6 +659,40 @@ static void ConvertToMeshOutputCompute(const ShaderReflection &refl, const SPIRV
   for(SPIRVIterator end = editor.EndEntries(); it < end; ++it)
     editor.Remove(it);
 
+  // Strip away any execution modes from the original shaders
+  for(it = editor.BeginEntries(); it < editor.BeginDebug(); ++it)
+  {
+    if(it.opcode() == spv::OpExecutionMode)
+    {
+      SPIRVId modeEntryID = SPIRVId(it.word(1));
+
+      // We only need to be cautious about what we are stripping for the entry
+      // that we are actually translating, the rest aren't used anyways.
+      if(modeEntryID == entryID)
+      {
+        // Lets check to make sure we don't blindly strip away execution modes that
+        // might actually have an impact on the behaviour of the shader.
+        spv::ExecutionMode execMode = spv::ExecutionMode(it.word(2));
+        switch(execMode)
+        {
+          case spv::ExecutionModeXfb: break;
+          default: RDCERR("Unexpected execution mode");
+        }
+      }
+
+      editor.PreModify(it);
+
+      SPIRVOperation op(it);
+
+      // invalid to have a nop here, but it will be stripped out later
+      op.nopRemove(1);
+      op[0] = SPV_NOP;
+
+      editor.PostModify(it);
+    }
+  }
+
+  // Add our compute shader execution mode
   editor.AddOperation(
       it, SPIRVOperation(spv::OpExecutionMode, {wrapperEntry, spv::ExecutionModeLocalSize,
                                                 MeshOutputDispatchWidth, 1, 1}));