Inconsistent use of diagnostic pragmas (-Wreturn-type)

[hirrolot]

Currently, inside match99, we emit the ... diagnostic push and ... diagnostic ignored "-Wreturn-type" pragmas, but without otherwise99 we won't return to the previous diagnostics state:

https://github.com/Hirrolot/datatype99/blob/e4c8e4688612cb63e471d7f7f1dcd358089ed467/datatype99.h#L154

I've spent some time trying to figure out how to automatically resolve this warning but with no success; therefore, the best solution for now is just don't suppress -Wreturn-type but to force a user to suppress it, if necessary.

FYI: The -Wreturn-type warning can be emitted due to the following reasons:

• A false positive due to the generation of single-step for-loops and the switch statement over a (conceptually) strict enumeration; see this SO question.
• C enumerations are seen by a compiler as ordinary integers -- see another SO question of mine.