tests: avoid testing syscall snippets if -DINTERCEPT_SYSCALL is not set

See https://bugs.debian.org/1007828

test/Makefile

@@ -13,6 +13,9 @@ ALL_TESTS = timetest test
 
 ifneq ($(filter -DINTERCEPT_SYSCALL,${CFLAGS}),)
 ALL_TESTS += confirm_variadic_promotion
+else
+TEST_SNIPPETS := $(filter-out syscall%,${TEST_SNIPPETS})
+EXPECTATIONS := $(filter-out syscall%,${EXPECTATIONS})
 endif
 
 all: $(ALL_TESTS)