[buffer] Add HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT

Fixes https://github.com/harfbuzz/harfbuzz/issues/3454
diff --git a/util/shape-options.hh b/util/shape-options.hh
index 806b34b..5a15c07 100644
--- a/util/shape-options.hh
+++ b/util/shape-options.hh
@@ -52,6 +52,7 @@
 				  (bot ? HB_BUFFER_FLAG_BOT : 0) |
 				  (eot ? HB_BUFFER_FLAG_EOT : 0) |
 				  (verify ? HB_BUFFER_FLAG_VERIFY : 0) |
+				  (unsafe_to_concat ? HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT : 0) |
 				  (preserve_default_ignorables ? HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES : 0) |
 				  (remove_default_ignorables ? HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES : 0) |
 				  0));
@@ -137,6 +138,7 @@
   hb_buffer_cluster_level_t cluster_level = HB_BUFFER_CLUSTER_LEVEL_DEFAULT;
   hb_bool_t normalize_glyphs = false;
   hb_bool_t verify = false;
+  hb_bool_t unsafe_to_concat = false;
   unsigned int num_iterations = 1;
 };
 
@@ -260,6 +262,7 @@
     {"utf8-clusters",	0, 0, G_OPTION_ARG_NONE,	&this->utf8_clusters,		"Use UTF8 byte indices, not char indices",	nullptr},
     {"cluster-level",	0, 0, G_OPTION_ARG_INT,		&this->cluster_level,		"Cluster merging level (default: 0)",	"0/1/2"},
     {"normalize-glyphs",0, 0, G_OPTION_ARG_NONE,	&this->normalize_glyphs,	"Rearrange glyph clusters in nominal order",	nullptr},
+    {"unsafe-to-concat",0, 0, G_OPTION_ARG_NONE,	&this->unsafe_to_concat,	"Produce unsafe-to-concat glyph flag",	nullptr},
     {"verify",		0, 0, G_OPTION_ARG_NONE,	&this->verify,			"Perform sanity checks on shaping results",	nullptr},
     {"num-iterations", 'n', G_OPTION_FLAG_IN_MAIN,
 			      G_OPTION_ARG_INT,		&this->num_iterations,		"Run shaper N times (default: 1)",	"N"},