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/Kbuild b/Kbuild
index 56b8edf..2d403cf 100644
--- a/Kbuild
+++ b/Kbuild
@@ -12,7 +12,7 @@
 
 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 @@
 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)