The BUILD_BUG_ON_ZERO() macro returns an (int)0 if it does not fail
at build time. LinuxKPI sort() has it as a guard for an unsupported
argument but ignores the return value.
This leads to gcc complaining:
error: statement with no effect [-Werror=unused-value]
Cast the result to (void) to silence the error as we are not interested
in it.
Reported by: CI
Sponsored by: The FreeBSD Foundation
MFC after: 3 days