Prepare to add new tests depending on the definitions

We want to be able to conditionally add tests.  This sets up to be
able to do that cleanly.

test/Makefile

@@ -9,7 +9,9 @@ OBJ = ${SRC:.c=.o}
 TEST_SNIPPETS = $(notdir $(basename $(wildcard snippets/*.c)))
 EXPECTATIONS= $(notdir $(basename $(wildcard snippets/*.variable)))
 
-all: timetest test
+ALL_TESTS = timetest test
+
+all: $(ALL_TESTS)
 
 .c.o:
 	${CC} -c ${CFLAGS} $<