kbuild: fix make incompatibility

"Paul Smith" <psmith@gnu.org> reported that we would fail
to build with a new check that may be enabled in an
upcoming version of make.

The error was:

      Makefile:442: *** mixed implicit and normal rules.  Stop.

The problem is that we did stuff like this:

config %config: ...

The solution was simple - the above was split into two with identical
prerequisites and commands.
With only three lines it was not worth to try to avoid the duplication.

Cc: "Paul Smith" <psmith@gnu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -439,7 +439,11 @@ ifeq ($(config-targets),1)
 include $(srctree)/arch/$(SRCARCH)/Makefile
 export KBUILD_DEFCONFIG KBUILD_KCONFIG
 
-config %config: scripts_basic outputmakefile FORCE
+config: scripts_basic outputmakefile FORCE
+	$(Q)mkdir -p include/linux include/config
+	$(Q)$(MAKE) $(build)=scripts/kconfig $@
+
+%config: scripts_basic outputmakefile FORCE
 	$(Q)mkdir -p include/linux include/config
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
 
@@ -1493,7 +1497,11 @@ endif
 	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
 
 # Modules
-/ %/: prepare scripts FORCE
+/: prepare scripts FORCE
+	$(cmd_crmodverdir)
+	$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
+	$(build)=$(build-dir)
+%/: prepare scripts FORCE
 	$(cmd_crmodverdir)
 	$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
 	$(build)=$(build-dir)