Gracefully handle no unicode in printf

tcshrc.prompt.defs

@@ -99,11 +99,16 @@ set referencechars_raw="${referencechars_raw} 262e"
 set prompt_hcolor=0
 set prompt_hsym=0
 
-set referencechars=()
-foreach ch ($referencechars_raw)
-    set unicode=`printf "\\u${ch}"`
-    set referencechars=( $referencechars `printf "${unicode}"` )
-end
+if( ! $?CSHENV_NO_UNICODE_PRINTF ) then
+	set referencechars=()
+	foreach ch ($referencechars_raw)
+		set unicode=`printf "\\u${ch}"`
+		set referencechars=( $referencechars `printf "${unicode}"` )
+	end
+else
+	# Safe fallback for when there's no unicode printf
+	set referencechars="A B C D X Y Z"
+endif
 
 # Rotation
 alias precmd 'source ${CSHENV_DIR}/tcshrc.prompt.final'