More C type errors by default for GCC 14

[Sam James]

Florian Weimer <fw@deneb.enyo.de> writes:

> [...]
> In summary, all these seems to be good candidates for errors by default:
>
> * int-conversion as errors (already raised separately
> * -Wint-conversion for ?:
> * parameter names in non-prototype function declarations
> * the union wait function pointer compatibility kludge
> * return-with-out-value for non-void functions
> * -Wincomatible-pointer-types warning for ?: (but no error yet, see below)
>
> This are more “maybe“:
>
> * incompatible-pointer-types as errors (already raised separately)
> * int-conversion and incompatible-pointer-types in comparisons
> * return with value in a function returning void

-Wreturn-type tends to bite people with C++. Obviously the behaviour
is different for C, but it's a serious code smell. I've been playing
with it for C for a while and I don't get that many hits with it of
this type.

> * dereferencing void *
> * taking the address of void

I think I've seen these but they've been accompanied by other issues.

> * "function types not truly compatible in ISO C"
>   and "types are not quite compatible" (depending on what they actually mean)
> * qualifier mismatches (may need separate opt-out)

This has been common for func. ptrs. but not too bad. I haven't
got any data on other cases but am a bit worried about how noisy it'll
be for those.

> * sign mismatches in pointers (definitely needs separate opt-out)
>
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