x86: Don't generate cmpxchg8b_emu if CONFIG_X86_CMPXCHG64=y

Conditionaly compile cmpxchg8b_emu.o and EXPORT_SYMBOL(cmpxchg8b_emu).

This reduces the kernel size a bit.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4AC43E7E.1000600@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/i386_ksyms_32.c

@@ -15,8 +15,10 @@ EXPORT_SYMBOL(mcount);
  * the export, but dont use it from C code, it is used
  * by assembly code and is not using C calling convention!
  */
+#ifndef CONFIG_X86_CMPXCHG64
 extern void cmpxchg8b_emu(void);
 EXPORT_SYMBOL(cmpxchg8b_emu);
+#endif
 
 /* Networking helper routines. */
 EXPORT_SYMBOL(csum_partial_copy_generic);

arch/x86/lib/Makefile

@@ -15,8 +15,10 @@ ifeq ($(CONFIG_X86_32),y)
         obj-y += atomic64_32.o
         lib-y += checksum_32.o
         lib-y += strstr_32.o
-        lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o
-
+        lib-y += semaphore_32.o string_32.o
+ifneq ($(CONFIG_X86_CMPXCHG64),y)
+        lib-y += cmpxchg8b_emu.o
+endif
         lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
 else
         obj-y += io_64.o iomap_copy_64.o