kbuild: move modpost out of 'scripts' target

I am eagar to build under the scripts/ directory only with $(HOSTCC),
but scripts/mod/ highly depends on the $(CC) and target arch headers.
That it why the 'scripts' target must depend on 'asm-generic',
'gcc-plugins', and $(autoksyms_h).

Move it to the 'prepare0' stage. I know this is a cheesy workaround,
but better than the current situation.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index bfab340..6da4631 100644
--- a/Makefile
+++ b/Makefile
@@ -1075,7 +1075,7 @@
 # Carefully list dependencies so we do not try to build scripts twice
 # in parallel
 PHONY += scripts
-scripts: scripts_basic scripts_dtc asm-generic gcc-plugins $(autoksyms_h)
+scripts: scripts_basic scripts_dtc
 	$(Q)$(MAKE) $(build)=$(@)
 
 # Things we need to do before we recursively start building the kernel
@@ -1113,6 +1113,7 @@
 archprepare: archheaders archscripts macroprepare scripts_basic gcc-plugins
 
 prepare0: archprepare
+	$(Q)$(MAKE) $(build)=scripts/mod
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..