Well, counterexample would be modern C compilers. They break old code left and right and while people occasionally complain about it the compiler authors have s

Well, counterexample would be modern C compilers. They break old code left and right and while people occasionally complain about it the compiler authors have strong support in the form of C standard and generally do not budge under the complaints. Occasionally a special flag is added for exceptional cases (hello -fwrapv -fno-strict-aliasing), but that is more like adding new feature to api than staying bug-compatible.