Fix warning in SECCOMP killing build.

Instead tell user what it means really.
This means that Travis can build with SECCOMP.

Author: Kubuxu

.travis.yml

@@ -17,5 +17,4 @@ sudo: false
 script:
   - "uname -a"
   - "bash node_build/run_jshint"
-    # travis' new container infrastructure's libc doesn't have SIGSYS signal info
-  - "Seccomp_NO=1 ./do"
+  - "./do"

util/Seccomp.c

@@ -19,6 +19,7 @@
 #include "util/Seccomp.h"
 #include "util/Bits.h"
 #include "util/ArchInfo.h"
+#include "util/Defined.h"
 
 // getpriority()
 #include <sys/resource.h>
@@ -51,14 +52,21 @@
 #if defined(si_syscall)
 # define GET_SYSCALL_NUM(si) ((si)->si_syscall)
 #else
-# warning "your libc doesn't define SIGSYS signal info! Try build witch Seccomp_NO=1"
+#pragma message "your libc doesn't define SIGSYS signal info! \
+info about syscall number in case of SECCOMP crash can be invalid"
 # define GET_SYSCALL_NUM(si) ((si)->si_value.sival_int)
 #endif
 
 static void catchViolation(int sig, siginfo_t* si, void* threadContext)
 {
     printf("Attempted banned syscall number [%d] see doc/Seccomp.md for more information\n",
            GET_SYSCALL_NUM(si));
+
+    if (Defined(si_syscall)) {
+        printf("Your libc doesn't define SIGSYS signal info. "
+               "Above information about syscall number can be invalid.\n");
+    }
+
     Assert_failure("Disallowed Syscall");
 }