Added executable list for all targets and print a message when certain

samples are not available for a target (instead of failing). This makes
"make SYS=<target>" in samples recursively work for all supported targets.

samples/tutorial/Makefile

@@ -31,10 +31,56 @@ else
   LD := $(if $(wildcard ../../bin/ld65*),../../bin/ld65,ld65)
 endif 
 
-samples: hello
+EXELIST_atari2600 = \
+	notavailable
+
+EXELIST_bbc = \
+	notavailable
+
+EXELIST_creativision = \
+	notavailable
+
+EXELIST_gamate = \
+	notavailable
+
+EXELIST_geos-cbm = \
+	notavailable
+
+EXELIST_geos-apple = \
+	notavailable
+
+EXELIST_lunix = \
+	notavailable
+
+EXELIST_lynx = \
+	notavailable
+
+EXELIST_nes = \
+	notavailable
+
+EXELIST_osic1p = \
+	notavailable
+
+EXELIST_pce = \
+	notavailable
+
+EXELIST_supervision = \
+	notavailable
+
+# Unlisted targets will try to build everything.
+# That lets us learn what they cannot build, and what settings
+# we need to use for programs that can be built and run.
+ifndef EXELIST_$(SYS)
+EXELIST_$(SYS) := ${patsubst %.c,%,$(wildcard *.c)}
+endif
+
+samples: $(EXELIST_$(SYS))
 
 hello: hello.c text.s
 	$(CL) -t $(SYS) -o hello hello.c text.s
 
+# empty target used to skip systems that will not work with any program in this dir
+notavailable:
+	@echo "warning: tutorial sample not available for" $(SYS)
 clean:
 	@$(DEL) hello 2>$(NULLDEV)