kbuild: Use LINUXINCLUDE to specify include/ directory

Peter Chubb <peterc@gelato.unsw.edu.au> reported that building i386
on a non-i386 platform failed, because gcc could not locate boot.h.
Root cause was the extra include2 directory used when using O=
to specify the output directory.
Added LINUXINCLUDE as a portable way to specify the include/
directory, and changed the two users.
This avoids hardcoding 'include2' in non-kbuild core files.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -294,9 +294,13 @@ AFLAGS_KERNEL	=
 
 NOSTDINC_FLAGS  = -nostdinc -iwithprefix include
 
-CPPFLAGS        := -D__KERNEL__ -Iinclude \
+# Use LINUXINCLUDE when you must reference the include/ directory.
+# Needed to be compatible with the O= option
+LINUXINCLUDE    := -Iinclude \
                    $(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include)
 
+CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)
+
 CFLAGS 		:= -Wall -Wstrict-prototypes -Wno-trigraphs \
 	  	   -fno-strict-aliasing -fno-common
 AFLAGS		:= -D__ASSEMBLY__
@@ -306,7 +310,7 @@ export	VERSION PATCHLEVEL SUBLEVEL EXTRAVERSION KERNELRELEASE ARCH \
 	CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE \
 	HOSTCXX HOSTCXXFLAGS LDFLAGS_BLOB LDFLAGS_MODULE CHECK
 
-export CPPFLAGS NOSTDINC_FLAGS OBJCOPYFLAGS LDFLAGS
+export CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
 export CFLAGS CFLAGS_KERNEL CFLAGS_MODULE 
 export AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 

arch/i386/boot/Makefile

@@ -31,7 +31,7 @@ subdir- 	:= compressed
 
 host-progs	:= tools/build
 
-HOSTCFLAGS_build.o := -Iinclude
+HOSTCFLAGS_build.o := $(LINUXINCLUDE)
 
 # ---------------------------------------------------------------------------
 

arch/ppc64/boot/Makefile

@@ -25,7 +25,7 @@ CROSS32_COMPILE ?=
 
 BOOTCC		:= $(CROSS32_COMPILE)gcc
 HOSTCC		:= gcc
-BOOTCFLAGS	:= $(HOSTCFLAGS) -Iinclude -fno-builtin 
+BOOTCFLAGS	:= $(HOSTCFLAGS) $(LINUXINCLUDE) -fno-builtin 
 BOOTAS		:= $(CROSS32_COMPILE)as
 BOOTAFLAGS	:= -D__ASSEMBLY__ $(BOOTCFLAGS) -traditional
 BOOTLD		:= $(CROSS32_COMPILE)ld