Fix _GNU_SOURCE redefined warning
Fix _GNU_SOURCE redefined warning

mcaleavya/bcc,iovisor/bcc,brendangregg/bcc,mcaleavya/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,iovisor/bcc,mcaleavya/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,mcaleavya/bcc,brendangregg/bcc,tuxology/bcc,tuxology/bcc