BUG/MINOR: cpu_topo: work around a small bug in musl's CPU_ISSET()

BUG/MINOR: cpu_topo: work around a small bug in musl's CPU_ISSET()

As found in GH issue #3103, CPU_ISSET() on musl 1.25 doesn't match the man
page which says it's returning an int. The reason is pretty simple, it's
a macro that operates on the bits directly and returns the result of the
bit field applied to the mask as an unsigned long. Bits above 31 will
simply be dropped if returned as an int, which causes CPUs 32..63 to
appear as absent from cpu_sets.

The fix is trivial, it consists in just comparing the result against zero
(i.e. turning it to a boolean), but before it's merged and deployed we'll
have to face such deployments, so better implement the same workaround
in the code here since we have access to the raw long value.

This workaround should be backported to 3.0.