Re: [PATCH 2/3] ci: avoid bare "gcc" for osx-gcc job

> I do think there's value in testing with both clang and gcc in
> general[1]. And there is _some_ code which is compiled only on macos
> and not elsewhere. So this would be our only chance for gcc to see it.
> But it seems like a pretty small return for an entire parallel job.
> Especially as I do not think it has uncovered anything interesting in
> the past (even when it was working).

> [1] Another quirk is that we run the whole test suite for both
>     compilers, which is probably overkill. The main value in comparing
>     gcc vs clang is that we don't use any constructs that the compiler
>     complains about. It's _possible_ for there to be a construct that
>     the compiler does not notice but which causes a runtime difference
>     (say, undefined behavior which happens to work out on one compiler),
>     but I think we're again hitting diminishing returns.