kbuild: modpost on vmlinux regardless of CONFIG_MODULES

Based on patch from: Magnus Damm <magnus@valinux.co.jp>
This has the advantage that all section mismatch checks are run regardless
of modules being enabled or not.

When running modpost on vmlinux output:
MODPOST vmlinux

When running modpost on modules output count of modules like this:
MODPOST 5 modules
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -736,6 +736,7 @@ endif # ifdef CONFIG_KALLSYMS
 # vmlinux image - including updated kernel symbols
 vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) $(kallsyms.o) FORCE
 	$(call if_changed_rule,vmlinux__)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
 	$(Q)rm -f .old_version
 
 # The actual objects are generated when descending, 

scripts/Makefile

@@ -19,7 +19,7 @@ always		:= $(hostprogs-y)
 hostprogs-y += unifdef
 
 subdir-$(CONFIG_MODVERSIONS) += genksyms
-subdir-$(CONFIG_MODULES)     += mod
+subdir-y                     += mod
 
 # Let clean descend into subdirs
 subdir-	+= basic kconfig package

scripts/Makefile.modpost

@@ -51,19 +51,25 @@ _modpost: $(modules)
 
 # Step 2), invoke modpost
 #  Includes step 3,4
-quiet_cmd_modpost = MODPOST
+quiet_cmd_modpost = MODPOST $(words $(filter-out vmlinux FORCE, $^)) modules
       cmd_modpost = scripts/mod/modpost            \
         $(if $(CONFIG_MODVERSIONS),-m)             \
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a,)  \
 	$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
 	$(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
 	$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
-	$(filter-out FORCE,$^)
+	$(wildcard vmlinux) $(filter-out FORCE,$^)
 
 PHONY += __modpost
-__modpost: $(wildcard vmlinux) $(modules:.ko=.o) FORCE
+__modpost: $(modules:.ko=.o) FORCE
 	$(call cmd,modpost)
 
+quiet_cmd_kernel-mod = MODPOST $@
+      cmd_kernel-mod = $(cmd_modpost)
+
+vmlinux: FORCE
+	$(call cmd,kernel-mod)
+
 # Declare generated files as targets for modpost
 $(symverfile):         __modpost ;
 $(modules:.ko=.mod.c): __modpost ;