Given:

  void func() { }
  void func() = delete;

Clang produces:

  spec.cpp:2:6: error: redefinition of 'func'
  void func() = delete;
       ^
  spec.cpp:1:6: note: previous definition is here
  void func() { }
       ^
  spec.cpp:2:15: error: deleted definition must be first declaration
  void func() = delete;
                ^
  spec.cpp:1:6: note: previous declaration is here
  void func() { }
       ^

Essentially the same diagnostic twice. Either we could simply suppress the second diagnostic when we know the function is already defined (& thus we already produced the first diagnostic), or suppress the first diagnostic when the new definition is deleted and, possibly, make the "deleted definition must be first" diagnostic have some more specific text for this case (based on the same property as the first option: that there's already a definition)