seccomp: add obsolete argument to command line

This patch introduces the argument [,obsolete=allow] to the `-sandbox on'
option. It allows Qemu to run safely on old system that still relies on
old system calls.

Signed-off-by: Eduardo Otubo <otubo@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 9f6e2ad..72150c6 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4017,13 +4017,21 @@
 ETEXI
 
 DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
-    "-sandbox <arg>  Enable seccomp mode 2 system call filter (default 'off').\n",
+    "-sandbox on[,obsolete=allow|deny]\n" \
+    "                Enable seccomp mode 2 system call filter (default 'off').\n" \
+    "                use 'obsolete' to allow obsolete system calls that are provided\n" \
+    "                    by the kernel, but typically no longer used by modern\n" \
+    "                    C library implementations.\n",
     QEMU_ARCH_ALL)
 STEXI
-@item -sandbox @var{arg}
+@item -sandbox @var{arg}[,obsolete=@var{string}]
 @findex -sandbox
 Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
 disable it.  The default is 'off'.
+@table @option
+@item obsolete=@var{string}
+Enable Obsolete system calls
+@end table
 ETEXI
 
 DEF("readconfig", HAS_ARG, QEMU_OPTION_readconfig,