Apply gap build fix for gcc-15

[vbraun]

Taken from https://src.fedoraproject.org/rpms/gap/blob/rawhide/f/gap-c23.patch

There might be gap packages that need to be fixed separately, but this at least lets us compile the base gap

[github-actions]

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[dimpase]

probably needs C standard guard for a preprocessor macro to put patch in, just like glpk

[vbraun]

I don't think there is any danger of breaking old compilers, the only actual change is

-typedef Obj (* ObjFunc) (/*arguments*/);
+typedef void *ObjFunc;

and thats as old as rocks. There is a longish preamble of the patch that mentions bool.c, but thats just for reference. Maybe you misread that?

[dimpase]

dunno, GAP people don't think it's as trivial.
There is an issue on their GitHub, can you find it?

[vbraun]

Upstream bug is this one: gap-system/gap#5857

The proper fix is probably to turn ObjFunc into a variadic function pointer, as discussed there. The patch here is just using an opaque pointer. It compiles (because nothing in gap ends up calling throught an ObjFunc pointer), but it is more of a bandaid than what I would consider a proper fix. Though good enough for now...

[dimpase]

OK, assuming it's not only compiles, but passes tests (the spkg as well as testlong)

[dimpase]

@orlitzky - do you have anything to say on this issue?