kbuild: rebuild .vmlinux.export.o when its prerequisite is updated

When include/linux/export-internal.h is updated, .vmlinux.export.o
must be rebuilt, but it does not happen because its rule is hidden
behind scripts/link-vmlinux.sh.

Move it out of the shell script, so that Make can see the dependency
between vmlinux and .vmlinux.export.o.

Move the vmlinux rule to scripts/Makefile.vmlinux.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -502,7 +502,7 @@ AFLAGS_MODULE   =
 LDFLAGS_MODULE  =
 CFLAGS_KERNEL	=
 AFLAGS_KERNEL	=
-LDFLAGS_vmlinux =
+export LDFLAGS_vmlinux =
 
 # Use USERINCLUDE when you must reference the UAPI directories only.
 USERINCLUDE    := \
@@ -1160,17 +1160,9 @@ vmlinux_o: vmlinux.a $(KBUILD_VMLINUX_LIBS)
 vmlinux.o modules.builtin.modinfo modules.builtin: vmlinux_o
 	@:
 
-ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
-
-# Final link of vmlinux with optional arch pass after final link
-cmd_link-vmlinux =                                                 \
-	$(CONFIG_SHELL) $< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)";    \
-	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
-
-vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) modpost FORCE
-	+$(call if_changed_dep,link-vmlinux)
-
-targets += vmlinux
+PHONY += vmlinux
+vmlinux: vmlinux.o $(KBUILD_LDS) modpost
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux
 
 # The actual objects are generated when descending,
 # make sure no implicit rule kicks in
@@ -1501,7 +1493,7 @@ endif # CONFIG_MODULES
 # Directories & files removed with 'make clean'
 CLEAN_FILES += include/ksym vmlinux.symvers modules-only.symvers \
 	       modules.builtin modules.builtin.modinfo modules.nsdeps \
-	       compile_commands.json .thinlto-cache .vmlinux.objs
+	       compile_commands.json .thinlto-cache .vmlinux.objs .vmlinux.export.c
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_FILES += include/config include/generated          \