x86: Add BITS to allow simple Makefile sharing

Preperatory patch to simplify the sharing of Makefiles in
arch/x86.

Linus came up with this during a discussion about the ugliness of
ifeq($CONFIG_X86_32),y) and obj-$(CONFIG_X86_32) in the shared
Makefiles.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/i386/Makefile

@@ -20,6 +20,12 @@
 # Fill in SRCARCH
 SRCARCH	:= x86
 
+# BITS is used as extension for files which are available in a 32 bit
+# and a 64 bit version to simplify shared Makefiles.
+# e.g.: obj-y += foo_$(BITS).o
+BITS := 32
+export BITS
+
 HAS_BIARCH      := $(call cc-option-yn, -m32)
 ifeq ($(HAS_BIARCH),y)
 AS              := $(AS) --32

arch/x86_64/Makefile

@@ -24,6 +24,12 @@
 # Fill in SRCARCH
 SRCARCH	:= x86
 
+# BITS is used as extension for files which are available in a 32 bit
+# and a 64 bit version to simplify shared Makefiles.
+# e.g.: obj-y += foo_$(BITS).o
+BITS := 64
+export BITS
+
 LDFLAGS		:= -m elf_x86_64
 OBJCOPYFLAGS	:= -O binary -R .note -R .comment -S
 LDFLAGS_vmlinux :=