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>
diff --git a/Makefile b/Makefile
index 4635a64..61e178f 100644
--- a/Makefile
+++ b/Makefile
@@ -186,7 +186,8 @@
 CROSS_COMPILE	?=
 
 # Architecture as present in compile.h
-UTS_MACHINE := $(ARCH)
+UTS_MACHINE 	:= $(ARCH)
+SRCARCH 	:= $(ARCH)
 
 KCONFIG_CONFIG	?= .config
 
@@ -322,7 +323,7 @@
 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 @@
 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