Here is my not-very-novel proposal for function overriding only. Its backward/forward compatible and free of name-mangling.

  void qsort_i8 ( i8 *ptr, int num);
  void qsort_i16(i16 *ptr, int num);
  void qsort_i32(i32 *ptr, int num);
  void qsort_i64(i64 *ptr, int num);
  
  #if __has_builtin(__builtin_overridable)
  __builtin_overridable(qsort, qsort_i8, qsort_i16); // qsort resolves to qsort_i8 qsort_i16
  // qsort() is forward compatible and upgradable with your own types
  __builtin_overridable(qsort, qsort_i32, qsort_i64); // qsort resolves to qsort_i8 qsort_i16 qsort_i32 qsort_i64 
  #endif
  
  i8  *ptr0; int num0;
  i16 *ptr1; int num1;
  i32 *ptr2; int num2;
  i64 *ptr3; int num3;
  
  qsort(ptr0, num0); // call qsort_i8()
  qsort(ptr1, num1); // call qsort_i16()
  qsort(ptr2, num2); // call qsort_i32()
  qsort(ptr3, num3); // call qsort_i64()