[PATCH] linux: Fix integer overflow warnings when including <sys/mount.h> [BZ #32708]

[Florian Weimer]

* Carlos O'Donell:

> - I still think using "1U << 31" is the clearest possible solution and
>   follows established precedent. You need a compiler that supports
>   unsigned enums and the full representable range to compile code in
>   the ecosystem.

I tend to agree for <sys/mount.h>.  In things like <math.h>, we should
aim for stricter conformance, but here it is okay.

Thanks,
Florian