Fix FreeBSD 14 build (#975)

Fix FreeBSD 14 build (#975)

FreeBSD 14 defines 3-parameter CPU_AND() macro as a `do {} while` loop.
Our (void) in front of that loop creates a syntax error.

    CpuAffinitySet.cc:41:16: error: expected expression
    (void) CPU_AND(&cpuSet, &cpuSet, &theOrigCpuSet);

That (void) was added in commit 7ec6d51 to "remove GNU-specific syntax",
but we cannot tell what specific problem that 10-year old change solved.
Known 3-parameter CPU_AND(3) documentation says the call returns void.