Add newfstatat to white list.

The newfstatat system call is used in glibc 2.33 during normal
operation. This fixes a core dump (which is expected behaviour when an
illegal system call is performed) spotted and reported by abbasmaheryar
on github.

Applied suggested fix by collidedscope on github as well.

See issue #28 for more details.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

seccomp.c

@@ -81,6 +81,7 @@ add_common_stage2_rules(scmp_filter_ctx ctx)
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mprotect), 0) ||
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0) ||
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(nanosleep), 0) ||
+	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(newfstatat), 0) ||
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(pipe), 0) ||
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(pipe2), 0) ||
 	    seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(poll), 0) ||