Return success for -M '?' query option.


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3008 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/vl.c b/vl.c
index 89a2a17..88f4177 100644
--- a/vl.c
+++ b/vl.c
@@ -6705,7 +6705,7 @@
 #endif
            DEFAULT_GDBSTUB_PORT,
            "/tmp/qemu.log");
-    exit(1);
+    exit(strcmp(optarg, "?"));
 }
 
 #define HAS_ARG 0x0001