Add an exclusion

Author: mernst

Makefile

@@ -10,6 +10,7 @@ clean:
 
 
 # Code style; defines `style-check` and `style-fix`.
+CODE_STYLE_EXCLUSIONS_USER := --exclude-dir subject-programs
 ifeq (,$(wildcard .plume-scripts))
 dummy := $(shell git clone -q https://github.com/plume-lib/plume-scripts.git .plume-scripts)
 endif