kbuild: generate modules.order only when CONFIG_MODULES=y

Backport from kernel although it is unused since it makes diffing easier.
commit 1d8001ef358 ("kbuild: generate modules.order only when CONFIG_MODULES=y")

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index ed58bca..2b2beb0 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -82,7 +82,9 @@
 builtin-target := $(obj)/built-in.o
 endif
 
+ifdef CONFIG_MODULES
 modorder-target := $(obj)/modules.order
+endif
 
 # We keep a list of all modules in $(MODVERDIR)