wow, it builds! added empty matrix.c and moved custom matrix code to custom_matrix.cpp

still untested because of hardware availability :(

keyboards/converter/usb_usb/matrix.c

@@ -0,0 +1 @@
+// Intentionally left empty. This file must exist for this board to build.

keyboards/converter/usb_usb/rules.mk

@@ -111,7 +111,7 @@ OPT_DEFS += -DBOOTLOADER_SIZE=4096
 
 CUSTOM_MATRIX = yes
 
-SRC = matrix.cpp
+SRC = custom_matrix.cpp
 
 #
 # Keymap file