[PATCH v2 1/2] build: don't export building_out_of_srctree

[Jan Beulich <jbeulich@xxxxxxxx>]

I don't view a variable of this name as suitable for exporting, the more
that it carries entirely redundant information. The reasons for its
introduction in Linux commit 051f278e9d81 ("kbuild: replace
KBUILD_SRCTREE with boolean building_out_of_srctree") also don't apply
to us. Ditch exporting of the variable, replacing uses suitably.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: New.
---
For further reasons (besides the similar redundancy aspect) exporting
VPATH looks also suspicious: Its name being all uppercase makes it a
"non application private" variable, i.e. it or its (pre-existing) value
may have a purpose/use elsewhere. And exporting it looks to be easily
avoidable: Instead of setting it in xen/Makefile, it looks like it could
be set in xen/scripts/Kbuild.include. Thoughts?

--- a/xen/Makefile
+++ b/xen/Makefile
@@ -208,7 +208,7 @@ endif
 objtree := .
 VPATH := $(srctree)
 
-export building_out_of_srctree srctree objtree VPATH
+export srctree objtree VPATH
 
 export XEN_ROOT := $(abs_srctree)/..
 
--- a/xen/arch/x86/boot/Makefile
+++ b/xen/arch/x86/boot/Makefile
@@ -14,7 +14,7 @@ $(obj)/head.o: $(head-bin-objs:.o=.bin)
 CFLAGS_x86_32 := $(subst -m64,-m32 -march=i686,$(XEN_TREEWIDE_CFLAGS))
 $(call cc-options-add,CFLAGS_x86_32,CC,$(EMBEDDED_EXTRA_CFLAGS))
 CFLAGS_x86_32 += -Werror -fno-builtin -g0 -msoft-float
-ifdef building_out_of_srctree
+ifneq ($(abs_objtree),$(abs_srctree))
 CFLAGS_x86_32 += -I$(objtree)/include
 endif
 CFLAGS_x86_32 += -I$(srctree)/include
--- a/xen/scripts/Makefile.host
+++ b/xen/scripts/Makefile.host
@@ -88,7 +88,7 @@ _hostcxx_flags = $(HOSTCXXFLAGS) $(HOST_
                  $(HOSTCXXFLAGS_$(target-stem).o)
 
 # $(objtree)/$(obj) for including generated headers from checkin source files
-ifdef building_out_of_srctree
+ifneq ($(abs_objtree),$(abs_srctree))
 _hostc_flags   += -I $(objtree)/$(obj)
 _hostcxx_flags += -I $(objtree)/$(obj)
 endif