%.import.so : %.import.scm
        $(CSC) $(CSC_FLAGS) -s $< -O2 -d0 -I $*/ -o $@
        @echo "\t-> $@"
        @echo ""

%.so %.import.scm : %.scm
        $(CSC) $(CSC_FLAGS) -s -O2 -d1 $^ -j $* -I $*/ -o $*.so
        @echo "\t-> $*.so"
        @echo "\t-> $*.import.scm"
        @echo ""


%.o : %.scm
        $(CSC) $(CSC_FLAGS) -c -O2 -d1 $@.scm -unit $@ -j $@

% : %.scm
        $(CSC) $(CSC_FLAGS) $<

If anything in the.app/* changes, then rebuild the app:

APPS=$(wildcard *.app)
APPS_DEPS=$(patsubst %,%.dep,$(APPS))

%.dep: %/
        echo "vpath $*.scm $*" > $@
        find $* -type f -print0 | sed -e 's/ /\\ /g' | xargs -0 echo "$*.import.so: " >> $@
        find $* -type f -print0 | sed -e 's/ /\\ /g' | xargs -0 echo "$*.so: " >> $@