Required to build the GTK interface.

diff -Nuar a/make/include/main.rules b/make/include/main.rules
--- a/make/include/main.rules	2024-02-13 14:21:08.536043130 +0000
+++ b/make/include/main.rules	2024-02-13 14:20:54.620043122 +0000
@@ -49,5 +49,6 @@
 ## build all dependency dirs
 $(sort $(dir $(BUILD.out))):
 	$(MKDIR.exe) -p $@
+	$(MKDIR.exe) -p	$(BUILD/)contrib/include/
 
 endif ## FEATURE.xcode XCODE.driver