kbuild: remove 'addtree' and 'flags' magic for header search paths

The 'addtree' and 'flags' in scripts/Kbuild.include are so compilecated
and ugly.

As I mentioned in [1], Kbuild should stop automatic prefixing of header
search path options.

I fixed up (almost) all Makefiles in the kernel. Now 'addtree' and
'flags' have been removed.

Kbuild still caters to add $(srctree)/$(src) and $(objtree)/$(obj)
to the header search path for O= building, but never touches extra
compiler options from ccflags-y etc.

[1]: https://patchwork.kernel.org/patch/9632347/

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 7484b9d..a675ce1 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -192,14 +192,6 @@
 # $(Q)$(MAKE) $(hdr-inst)=dir
 hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj
 
-# Prefix -I with $(srctree) if it is not an absolute path.
-# skip if -I has no parameter
-addtree = $(if $(patsubst -I%,%,$(1)), \
-$(if $(filter-out -I/% -I./% -I../%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1)),$(1)),$(1))
-
-# Find all -I options and call addtree
-flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))
-
 # echo command.
 # Short version is used, if $(quiet) equals `quiet_', otherwise full one.
 echo-cmd = $(if $($(quiet)cmd_$(1)),\
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 73b8041..b6a54bd 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -67,18 +67,16 @@
 _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(basetarget).o)
 
-__hostc_flags	= $(_hostc_flags)
-__hostcxx_flags	= $(_hostcxx_flags)
-
+# $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
 ifneq ($(srctree),.)
-__hostc_flags	= -I$(obj) $(call flags,_hostc_flags)
-__hostcxx_flags	= -I$(obj) $(call flags,_hostcxx_flags)
+_hostc_flags   += -I $(objtree)/$(obj)
+_hostcxx_flags += -I $(objtree)/$(obj)
 endif
 endif
 
-hostc_flags    = -Wp,-MD,$(depfile) $(__hostc_flags)
-hostcxx_flags  = -Wp,-MD,$(depfile) $(__hostcxx_flags)
+hostc_flags    = -Wp,-MD,$(depfile) $(_hostc_flags)
+hostcxx_flags  = -Wp,-MD,$(depfile) $(_hostcxx_flags)
 
 #####
 # Compile programs on the host
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 41e98fa..1b412d4 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -137,36 +137,26 @@
 	$(CFLAGS_KCOV))
 endif
 
-__c_flags	= $(_c_flags)
-__a_flags	= $(_a_flags)
-__cpp_flags     = $(_cpp_flags)
-
-# If building the kernel in a separate objtree expand all occurrences
-# of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
+# $(srctree)/$(src) for including checkin headers from generated source files
+# $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
 ifneq ($(srctree),.)
-
-# -I$(obj) locates generated .h files
-# $(call addtree,-I$(obj)) locates .h files in srctree, from generated .c files
-#   and locates generated .h files
-# FIXME: Replace both with specific CFLAGS* statements in the makefiles
-__c_flags	= $(if $(obj),$(call addtree,-I$(src)) -I$(obj)) \
-		  $(call flags,_c_flags)
-__a_flags	= $(call flags,_a_flags)
-__cpp_flags     = $(call flags,_cpp_flags)
+_c_flags   += -I $(srctree)/$(src) -I $(objtree)/$(obj)
+_a_flags   += -I $(srctree)/$(src) -I $(objtree)/$(obj)
+_cpp_flags += -I $(srctree)/$(src) -I $(objtree)/$(obj)
 endif
 endif
 
 c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 		 -include $(srctree)/include/linux/compiler_types.h       \
-		 $(__c_flags) $(modkern_cflags)                           \
+		 $(_c_flags) $(modkern_cflags)                           \
 		 $(basename_flags) $(modname_flags)
 
 a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
-		 $(__a_flags) $(modkern_aflags)
+		 $(_a_flags) $(modkern_aflags)
 
 cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
-		 $(__cpp_flags)
+		 $(_cpp_flags)
 
 ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F))