[XEN PATCH 15/15] build: remove Config.mk include from Rules.mk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

Everything needed to build the hypervisor should already be configured
by "xen/Makefile", thus Config.mk shouldn't be needed.

Then, Config.mk keeps on testing support of some CFLAGS with CC, the
result of this testing is not used at this stage so the build is
slowed unnecessarily.

Likewise, GCC is checked to be at the minimum at 4.2 when entering
every sub-directory, so the check have run countless time at this
stage.

We only need to export a few more configuration variables. And add
some variables in Kbuild.include, and macro fallbacks for Make older
than 3.81. (Adding `or` just in case. it's only used in xen/Makefile,
which includes Config.mk and so has already the fallback.)

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---

Notes:
    Removing Config.mk benefit:
        Rebuild on my computer is aboud 1 second faster overall.
        Save maybe 3 seconds of user time
        system less loaded

 xen/Makefile               | 4 ++++
 xen/Rules.mk               | 1 -
 xen/scripts/Kbuild.include | 7 +++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/xen/Makefile b/xen/Makefile
index 4dc3acf2a6..9af7223c66 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -246,10 +246,14 @@ export TARGET_ARCH     := $(shell echo $(XEN_TARGET_ARCH) 
| \
                             sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g' \
                                 -e s'/riscv.*/riscv/g')
 
+export XEN_COMPILE_ARCH XEN_TARGET_ARCH
 export CONFIG_SHELL := $(SHELL)
 export CC CXX LD NM OBJCOPY OBJDUMP ADDR2LINE
+export CPP AR
 export YACC = $(if $(BISON),$(BISON),bison)
 export LEX = $(if $(FLEX),$(FLEX),flex)
+export HOSTCC HOSTCXX HOSTCFLAGS
+export EMBEDDED_EXTRA_CFLAGS LDFLAGS_DIRECT
 
 # Default file for 'make defconfig'.
 export KBUILD_DEFCONFIG := $(ARCH)_defconfig
diff --git a/xen/Rules.mk b/xen/Rules.mk
index 8177d405c3..8291e0a573 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -17,7 +17,6 @@ __build:
 
 -include $(objtree)/include/config/auto.conf
 
-include $(XEN_ROOT)/Config.mk
 include $(srctree)/scripts/Kbuild.include
 include $(XEN_ROOT)/config/compiler-testing.mk
 
diff --git a/xen/scripts/Kbuild.include b/xen/scripts/Kbuild.include
index d820595e2f..dfa66f2c8a 100644
--- a/xen/scripts/Kbuild.include
+++ b/xen/scripts/Kbuild.include
@@ -8,6 +8,13 @@ empty   :=
 space   := $(empty) $(empty)
 space_escape := _-_SPACE_-_
 pound   := \#
+comma   := ,
+open    := (
+close   := )
+
+# fallbacks for GNU Make older than 3.81
+realpath = $(wildcard $(foreach file,$(1),$(shell cd -P $(dir $(file)) && echo 
"$$PWD/$(notdir $(file))")))
+or       = $(if $(strip $(1)),$(1),$(if $(strip $(2)),$(2),$(if $(strip 
$(3)),$(3),$(if $(strip $(4)),$(4)))))
 
 ###
 # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
-- 
Anthony PERARD