kbuild: remove src and obj from the top Makefile

Replace $(src) and $(obj) with $(srctree) and $(objtree), respectively.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arc/Makefile

@@ -18,7 +18,7 @@ ifdef CONFIG_ARC_CURR_IN_REG
 # any kernel headers, and missing the r25 global register
 # Can't do unconditionally because of recursive include issues
 # due to <linux/thread_info.h>
-LINUXINCLUDE	+=  -include ${src}/arch/arc/include/asm/current.h
+LINUXINCLUDE	+=  -include $(srctree)/arch/arc/include/asm/current.h
 endif
 
 cflags-y				+= -fsection-anchors