Clang: Decrease order of snippets

The order is 0 by default and thus the snippet items were at the very
top, e.g.:

  enum EnumType { EnumValue };

  void f()
  {
      EnumType et = // Complete here and see snippet items at top
  }

Change-Id: I70a160d102b91a2589972354c50aa5f0b29323e8
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cpptools/cppcompletionassistprocessor.h

@@ -45,7 +45,7 @@ namespace CppTools {
 class CPPTOOLS_EXPORT CppCompletionAssistProcessor : public TextEditor::IAssistProcessor
 {
 public:
-    CppCompletionAssistProcessor();
+    CppCompletionAssistProcessor(int snippetItemOrder = 0);
 
 protected:
     void addSnippets();