support out-of-tree build

by replacing `src` variable in Kbuild files.

Makefile.kbuild

@@ -3,7 +3,7 @@
 # ```
 # include $(top_srcdir)/Makefile.kbuild
 # ```
-KBUILD = $(MAKE) -C "$(LINUX_SOURCE_DIR)" M="$(abs_srcdir)" INSTALL_MOD_DIR="$(INSTALL_MOD_DIR)"
+KBUILD = $(MAKE) -C "$(LINUX_SOURCE_DIR)" M="$(abs_builddir)" INSTALL_MOD_DIR="$(INSTALL_MOD_DIR)"
 
 
 modules:

devices/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 REV := $(shell if test -s $(src)/../revision; then \
 		cat $(src)/../revision; \
 	else \

devices/ccat/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 TOPDIR := $(src)/../..
 
 ifeq (@ENABLE_CCAT@,1)

devices/e1000/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 TOPDIR := $(src)/../..
 
 REV := $(shell if test -s $(TOPDIR)/revision; then \

devices/e1000e/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 TOPDIR := $(src)/../..
 
 REV := $(shell if test -s $(TOPDIR)/revision; then \

devices/igb/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 TOPDIR := $(src)/../..
 
 REV := $(shell if test -s $(TOPDIR)/revision; then \

examples/dc_rtai/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 obj-m := ec_dc_rtai_sample.o
 
 ec_dc_rtai_sample-objs := dc_rtai_sample.o

examples/mini/Kbuild.in

@@ -31,6 +31,8 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+
 obj-m := ec_mini.o
 
 ec_mini-objs := mini.o

examples/rtai/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 obj-m := ec_rtai_sample.o
 
 ec_rtai_sample-objs := rtai_sample.o

examples/tty/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 obj-m := ec_tty_example.o
 
 ec_tty_example-objs := \

master/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 obj-m := ec_master.o
 
 ec_master-objs := \

tty/Kbuild.in

@@ -31,6 +31,9 @@
 #
 #------------------------------------------------------------------------------
 
+src := @abs_srcdir@
+ccflags-y := -I@abs_top_builddir@
+
 obj-m := ec_tty.o
 
 ec_tty-objs := \