kbuild: use in-kernel unifdef

Let headers_install use in-kernel unifdef
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -893,8 +893,8 @@ INSTALL_HDR_PATH=$(objtree)/usr
 export INSTALL_HDR_PATH
 
 PHONY += headers_install
-headers_install: include/linux/version.h
-	$(Q)unifdef -Ux /dev/null
+headers_install: include/linux/version.h scripts_basic FORCE
+	$(Q)$(MAKE) $(build)=scripts scripts/unifdef
 	$(Q)rm -rf $(INSTALL_HDR_PATH)/include
 	$(Q)$(MAKE) -rR -f $(srctree)/scripts/Makefile.headersinst obj=include
 

scripts/Makefile

@@ -15,6 +15,9 @@ hostprogs-$(CONFIG_IKCONFIG)     += bin2c
 
 always		:= $(hostprogs-y)
 
+# The following hostprogs-y programs are only build on demand
+hostprogs-y += unifdef
+
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-$(CONFIG_MODULES)     += mod
 

scripts/Makefile.headersinst

@@ -7,7 +7,7 @@
 #
 # ==========================================================================
 
-UNIFDEF := unifdef -U__KERNEL__
+UNIFDEF := scripts/unifdef -U__KERNEL__
 
 # Eliminate the contents of (and inclusions of) compiler.h
 HDRSED  := sed 	-e "s/ inline / __inline__ /g" \