Kbuild: allow arch/xxx to use a different source path

Preparatory patch for the source merge of arch/i386 and arch/x86_64
into arch/x86. This allows to keep the original arch directories as
stubs for the main Makefiles, Kconfigs et. al during the transition
phase while having the code in the new arch/x86 directory.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Kbuild

@@ -12,7 +12,7 @@ offsets-file := include/asm-$(ARCH)/asm-offsets.h
 
 always  := $(offsets-file)
 targets := $(offsets-file)
-targets += arch/$(ARCH)/kernel/asm-offsets.s
+targets += arch/$(SRCARCH)/kernel/asm-offsets.s
 clean-files := $(addprefix $(objtree)/,$(targets))
 
 # Default sed regexp - multiline due to syntax constraints
@@ -40,11 +40,11 @@ define cmd_offsets
 endef
 
 # We use internal kbuild rules to avoid the "is up to date" message from make
-arch/$(ARCH)/kernel/asm-offsets.s: arch/$(ARCH)/kernel/asm-offsets.c FORCE
+arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c FORCE
 	$(Q)mkdir -p $(dir $@)
 	$(call if_changed_dep,cc_s_c)
 
-$(obj)/$(offsets-file): arch/$(ARCH)/kernel/asm-offsets.s Kbuild
+$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s Kbuild
 	$(Q)mkdir -p $(dir $@)
 	$(call cmd,offsets)
 

Makefile

@@ -187,6 +187,7 @@ CROSS_COMPILE	?=
 
 # Architecture as present in compile.h
 UTS_MACHINE 	:= $(ARCH)
+SRCARCH 	:= $(ARCH)
 
 KCONFIG_CONFIG	?= .config
 
@@ -322,7 +323,7 @@ KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
 KERNELVERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
 
 export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
-export ARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
+export ARCH SRCARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE
 export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
@@ -609,7 +610,7 @@ libs-y		:= $(libs-y1) $(libs-y2)
 vmlinux-init := $(head-y) $(init-y)
 vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
 vmlinux-all  := $(vmlinux-init) $(vmlinux-main)
-vmlinux-lds  := arch/$(ARCH)/kernel/vmlinux.lds
+vmlinux-lds  := arch/$(SRCARCH)/kernel/vmlinux.lds
 export KBUILD_VMLINUX_OBJS := $(vmlinux-all)
 
 # Rule to link vmlinux - also used during CONFIG_KALLSYMS