kbuild: expand -I in KBUILD_CPPFLAGS

kbuild failed to expand include flags in KBUILD_CPPFLAGS
resulting in code like this in arch Makefiles:

ifeq ($(KBUILD_SRC),)
KBUILD_CPPFLAGS += -Iinclude/foo
else
KBUILD_CPPFLAGS += -I$(srctree)/include/foo
endif

Move use of LINUXINCLUDE into Makefile.lib to allow
us to expand -I directives of KBUILD_CPPFLAGS so
we can avoid the above code.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -336,7 +336,7 @@ LINUXINCLUDE    := -Iinclude \
                    -I$(srctree)/arch/$(hdr-arch)/include               \
                    -include include/linux/autoconf.h
 
-KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXINCLUDE)
+KBUILD_CPPFLAGS := -D__KERNEL__
 
 KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -fno-common \
@@ -1638,7 +1638,7 @@ cmd_crmodverdir = $(Q)mkdir -p $(MODVERDIR) \
                   $(if $(KBUILD_MODULES),; rm -f $(MODVERDIR)/*)
 
 a_flags = -Wp,-MD,$(depfile) $(KBUILD_AFLAGS) $(AFLAGS_KERNEL) \
-	  $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
+	  $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(KBUILD_CPPFLAGS) \
 	  $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
 
 quiet_cmd_as_o_S = AS      $@

scripts/Makefile.lib

@@ -104,9 +104,11 @@ else
 debug_flags =
 endif
 
-orig_c_flags   = $(KBUILD_CFLAGS) $(ccflags-y) $(CFLAGS_$(basetarget).o)
+orig_c_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)                     \
+                 $(ccflags-y) $(CFLAGS_$(basetarget).o)
 _c_flags       = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(orig_c_flags))
-_a_flags       = $(KBUILD_AFLAGS) $(asflags-y) $(AFLAGS_$(basetarget).o)
+_a_flags       = $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS)                     \
+                 $(asflags-y) $(AFLAGS_$(basetarget).o)
 _cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(@F))
 
 # If building the kernel in a separate objtree expand all occurrences
@@ -127,15 +129,16 @@ __a_flags	=                          $(call flags,_a_flags)
 __cpp_flags     =                          $(call flags,_cpp_flags)
 endif
 
-c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
+c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 		 $(__c_flags) $(modkern_cflags)                           \
 		 -D"KBUILD_STR(s)=\#s" $(basename_flags) $(modname_flags) \
 		  $(debug_flags)
 
-a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
+a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 		 $(__a_flags) $(modkern_aflags)
 
-cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)
+cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
+		 $(__cpp_flags)
 
 ld_flags       = $(LDFLAGS) $(ldflags-y)