Issue warning when deprecated -tdf option is used

Releases of qemu-kvm will be interrupted at qemu 1.3.0.
Users should switch to plain qemu releases.
To avoid breaking scenarios which are setup with command line
options specific to qemu-kvm, port these switches from qemu-kvm
to qemu.git.

Port -tdf option.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

vl.c

@@ -3280,6 +3280,10 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_semihosting:
                 semihosting_enabled = 1;
                 break;
+            case QEMU_OPTION_tdf:
+                fprintf(stderr, "Warning: user space PIT time drift fix "
+                                "is no longer supported.\n");
+                break;
             case QEMU_OPTION_name:
                 qemu_name = g_strdup(optarg);
 		 {