kbuild: revert "save ARCH & CROSS_COMPILE ..."

Revert commit 57554334

It caused following issues:

- On architectures where ARCH= setting is used to select between
  32 and 64 bit this was no longer possible without "make mrproper"
- If ARCH was changed then kbuild refused to run "make mrproper"
  because ARCH had changed
- When CROSS_COMPILE was changed people were asked to run "make mrproper"
  but kbuild refused to run "make mrproper" because CROSS_COMPILE changed.
- Spaces in CROSS_COMPILE was not 'supported'
- If an non-existing ARCH= was used kbuild could get stuck

Lessons learned:
. Despite being simple and straghtforward people uses very different
  approaches when building the kernel.

. CROSS_COMPILE is sometimes used for ccache despite cache being
  only a CC frontend so one would have expected CC to be
  used for this purpose.

. And obviously this was not tested widely enough.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

Makefile

@@ -179,46 +179,9 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
 # Alternatively CROSS_COMPILE can be set in the environment.
 # Default value for CROSS_COMPILE is not to prefix executables
 # Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile
-#
-# To force ARCH and CROSS_COMPILE settings include kernel.* files
-# in the kernel tree - do not patch this file.
 export KBUILD_BUILDHOST := $(SUBARCH)
-
-# Kbuild save the ARCH and CROSS_COMPILE setting in kernel.* files.
-# Restore these settings and check that user did not specify
-# conflicting values.
-
-saved_arch  := $(shell cat include/generated/kernel.arch  2> /dev/null)
-saved_cross := $(shell cat include/generated/kernel.cross 2> /dev/null)
-
-ifneq ($(CROSS_COMPILE),)
-        ifneq ($(saved_cross),)
-                ifneq ($(CROSS_COMPILE),$(saved_cross))
-                        $(error CROSS_COMPILE changed from \
-                                "$(saved_cross)" to \
-                                 to "$(CROSS_COMPILE)". \
-                                 Use "make mrproper" to fix it up)
-                endif
-        endif
-else
-    CROSS_COMPILE := $(saved_cross)
-endif
-
-ifneq ($(ARCH),)
-        ifneq ($(saved_arch),)
-                ifneq ($(saved_arch),$(ARCH))
-                        $(error ARCH changed from \
-                                "$(saved_arch)" to "$(ARCH)". \
-                                 Use "make mrproper" to fix it up)
-                endif
-        endif
-else
-        ifneq ($(saved_arch),)
-                ARCH := $(saved_arch)
-        else
-                ARCH := $(SUBARCH)
-        endif
-endif
+ARCH		?= $(SUBARCH)
+CROSS_COMPILE	?=
 
 # Architecture as present in compile.h
 UTS_MACHINE 	:= $(ARCH)
@@ -483,11 +446,6 @@ ifeq ($(config-targets),1)
 include $(srctree)/arch/$(SRCARCH)/Makefile
 export KBUILD_DEFCONFIG KBUILD_KCONFIG
 
-# save ARCH & CROSS_COMPILE settings
-$(shell mkdir -p include/generated &&                            \
-        echo $(ARCH)          > include/generated/kernel.arch && \
-        echo $(CROSS_COMPILE) > include/generated/kernel.cross)
-
 config: scripts_basic outputmakefile FORCE
 	$(Q)mkdir -p include/linux include/config
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@