linux/seccomp: fail nicely if siginfo_t->si_syscall is not defined
linux/seccomp: fail nicely if siginfo_t->si_syscall is not defined

Ubuntu 12.04 LTS (used by travis-ci.org) provides seccomp.h but does not
define si_syscall in siginfo_t structure in /usr/include/bits/siginfo.h.

fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared