Add a dummy argument `--enable-intrabc-ext` to support CTCv6.

This argument has no effect.
diff --git a/apps/aomenc.c b/apps/aomenc.c
index c4a68cb..39a780d 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -434,6 +434,7 @@
 #if CONFIG_SDP
   &g_av1_codec_arg_defs.enable_sdp,
 #endif
+  &g_av1_codec_arg_defs.enable_intrabc_ext,
   NULL,
 };
 
diff --git a/av1/arg_defs.c b/av1/arg_defs.c
index 86cc344..0ebc020 100644
--- a/av1/arg_defs.c
+++ b/av1/arg_defs.c
@@ -439,6 +439,9 @@
   .enable_intrabc = ARG_DEF(NULL, "enable-intrabc", 1,
                             "Enable intra block copy prediction mode "
                             "(0: false, 1: true (default))"),
+  .enable_intrabc_ext =
+      ARG_DEF(NULL, "enable-intrabc-ext", 1,
+              "Dummy argument to support CTCv6 command-line. Has no effect."),
   .enable_angle_delta =
       ARG_DEF(NULL, "enable-angle-delta", 1,
               "Enable intra angle delta (0: false, 1: true (default))"),
diff --git a/av1/arg_defs.h b/av1/arg_defs.h
index 6cbe5ef..62c0885 100644
--- a/av1/arg_defs.h
+++ b/av1/arg_defs.h
@@ -169,6 +169,7 @@
   arg_def_t enable_overlay;
   arg_def_t enable_palette;
   arg_def_t enable_intrabc;
+  arg_def_t enable_intrabc_ext;
   arg_def_t enable_angle_delta;
   arg_def_t enable_trellis_quant;
   arg_def_t enable_qm;
diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index 4200e96..90718ac 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -762,10 +762,9 @@
   cfg->enable_cdef = extra_cfg->enable_cdef;
   cfg->enable_restoration = extra_cfg->enable_restoration;
   cfg->superblock_size =
-      (extra_cfg->superblock_size == AOM_SUPERBLOCK_SIZE_64X64)
-          ? 64
-          : (extra_cfg->superblock_size == AOM_SUPERBLOCK_SIZE_128X128) ? 128
-                                                                        : 0;
+      (extra_cfg->superblock_size == AOM_SUPERBLOCK_SIZE_64X64)     ? 64
+      : (extra_cfg->superblock_size == AOM_SUPERBLOCK_SIZE_128X128) ? 128
+                                                                    : 0;
   cfg->enable_warped_motion = extra_cfg->enable_warped_motion;
 #if !CONFIG_REMOVE_DIST_WTD_COMP
   cfg->enable_dist_wtd_comp = extra_cfg->enable_dist_wtd_comp;
@@ -812,11 +811,10 @@
   extra_cfg->enable_deblocking = cfg->enable_deblocking;
   extra_cfg->enable_cdef = cfg->enable_cdef;
   extra_cfg->enable_restoration = cfg->enable_restoration;
-  extra_cfg->superblock_size = (cfg->superblock_size == 64)
-                                   ? AOM_SUPERBLOCK_SIZE_64X64
-                                   : (cfg->superblock_size == 128)
-                                         ? AOM_SUPERBLOCK_SIZE_128X128
-                                         : AOM_SUPERBLOCK_SIZE_DYNAMIC;
+  extra_cfg->superblock_size =
+      (cfg->superblock_size == 64)    ? AOM_SUPERBLOCK_SIZE_64X64
+      : (cfg->superblock_size == 128) ? AOM_SUPERBLOCK_SIZE_128X128
+                                      : AOM_SUPERBLOCK_SIZE_DYNAMIC;
   extra_cfg->enable_warped_motion = cfg->enable_warped_motion;
 #if !CONFIG_REMOVE_DIST_WTD_COMP
   extra_cfg->enable_dist_wtd_comp = cfg->enable_dist_wtd_comp;
@@ -3471,6 +3469,10 @@
   } else if (arg_match_helper(&arg, &g_av1_codec_arg_defs.enable_intrabc, argv,
                               err_string)) {
     extra_cfg.enable_intrabc = arg_parse_int_helper(&arg, err_string);
+  } else if (arg_match_helper(&arg, &g_av1_codec_arg_defs.enable_intrabc_ext,
+                              argv, err_string)) {
+    const int enable_intrabc_ext = arg_parse_int_helper(&arg, err_string);
+    (void)enable_intrabc_ext;
   } else if (arg_match_helper(&arg, &g_av1_codec_arg_defs.enable_angle_delta,
                               argv, err_string)) {
     extra_cfg.enable_angle_delta = arg_parse_int_helper(&arg, err_string);