Add wait4 to the seccomp2 sandbox allowable syscall list

fixes bug 15088. patch from sanic.

changes/bug15088

+  o Minor bugfixes (Linux seccomp2 sandbox):
+    - Upon receiving sighup, do not crash during attempts to call
+      wait4. Fixes bug 15088; bugfix on 0.2.5.1-alpha. Patch from
+      "sanic".

src/common/sandbox.c

@@ -164,6 +164,7 @@ static int filter_nopar_gen[] = {
 #endif
     SCMP_SYS(stat),
     SCMP_SYS(uname),
+    SCMP_SYS(wait4),
     SCMP_SYS(write),
     SCMP_SYS(writev),
     SCMP_SYS(exit_group),