kbuild: fix section mismatch check for vmlinux

vmlinux does not contain relocation entries which is
used by the section mismatch checks.
Reported by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>

Use the individual objects as inputs to overcome
this limitation.
In modpost check the .o files and skip non-ELF files.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 65e0a79..d5bbbcc 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -63,16 +63,16 @@
 	$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
 	$(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
 	$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
-	$(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w) \
-	$(wildcard vmlinux) $(filter-out FORCE,$^)
+	$(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
 
 PHONY += __modpost
 __modpost: $(modules:.ko=.o) FORCE
-	$(call cmd,modpost)
+	$(call cmd,modpost) $(wildcard vmlinux) $(filter-out FORCE,$^)
 
 quiet_cmd_kernel-mod = MODPOST $@
-      cmd_kernel-mod = $(cmd_modpost)
+      cmd_kernel-mod = $(cmd_modpost) $(KBUILD_VMLINUX_OBJS)
 
+PHONY += vmlinux
 vmlinux: FORCE
 	$(call cmd,kernel-mod)