test-depmod: avoid warning when we don't have zlib

testsuite/test-depmod.c:31:21: warning: ‘depmod_modules_order_for_compressed’ defined but not used [-Wunused-function]
 static noreturn int depmod_modules_order_for_compressed(const struct test *t)
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/testsuite/test-depmod.c b/testsuite/test-depmod.c
index 732a9d0..b9beb01 100644
--- a/testsuite/test-depmod.c
+++ b/testsuite/test-depmod.c
@@ -25,6 +25,7 @@
 
 #include "testsuite.h"
 
+#ifdef ENABLE_ZLIB
 #define MODULES_ORDER_UNAME "4.4.4"
 #define MODULES_ORDER_ROOTFS TESTSUITE_ROOTFS "test-depmod/modules-order-compressed"
 #define MODULES_ORDER_LIB_MODULES MODULES_ORDER_ROOTFS "/lib/modules/" MODULES_ORDER_UNAME
@@ -40,7 +41,6 @@
 	exit(EXIT_FAILURE);
 }
 
-#ifdef ENABLE_ZLIB
 DEFINE_TEST(depmod_modules_order_for_compressed,
 	.description = "check if depmod let aliases in right order when using compressed modules",
 	.config = {