kbuild: fix make O=...

kbuild failed to locate Kbuild.include.
Teach kbuild how to find Kbuild files when using make O=...

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
---
diff --git a/Makefile b/Makefile
index 7c607dc..ed1f4b5 100644
--- a/Makefile
+++ b/Makefile
@@ -310,7 +310,7 @@
 MAKEFLAGS += --include-dir=$(srctree)
 
 # We need some generic definitions
-include scripts/Kbuild.include
+include  $(srctree)/scripts/Kbuild.include
 
 # For maximum performance (+ possibly random breakage, uncomment
 # the following)
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index ebed6a4..8f4f5a3 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -10,7 +10,9 @@
 # Read .config if it exist, otherwise ignore
 -include .config
 
-include $(if $(wildcard $(obj)/Kbuild), $(obj)/Kbuild, $(obj)/Makefile)
+# The filename Kbuild has precedence over Makefile
+include $(if $(wildcard $(srctree)/$(src)/Kbuild), \
+                        $(srctree)/$(src)/Kbuild, $(srctree)/$(src)/Makefile)
 
 include scripts/Kbuild.include
 include scripts/Makefile.lib
diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
index ff3e87d..9c978b7 100644
--- a/scripts/Makefile.clean
+++ b/scripts/Makefile.clean
@@ -7,7 +7,9 @@
 .PHONY: __clean
 __clean:
 
-include $(if $(wildcard $(obj)/Kbuild), $(obj)/Kbuild, $(obj)/Makefile)
+# The filename Kbuild has precedence over Makefile
+include $(if $(wildcard $(srctree)/$(src)/Kbuild), \
+                        $(srctree)/$(src)/Kbuild, $(srctree)/$(src)/Makefile)
 
 # Figure out what we need to build from the various variables
 # ==========================================================================