This introduces a new flag ignored-reference-qualifiers for the existing "'A' qualifier on reference type B has no effect" diagnostic, as a child of ignored-qualifiers.
Rationale:
This particular diagnostic is enabled by default, but other parts of ignored-qualifiers are not. Anecdotally, a user may encounter this diagnostic in the wild, and, seeing it to be valuable, might try to raise it to error with -Werror=ignored-qualifiers, whereupon the other diagnostics the flag covers will also be raised, to the user's surprise and confusion. By splitting this diagnostic out into a separate flag, and marking it as a child of ignored-qualifiers, we allow the user more granular control of the diagnostics they care about, while maintaining backwards compatibility with existing build scripts.