x86: fix csum_partial() export

Fix this symbol export problem:

    Building modules, stage 2.
    MODPOST 193 modules
    ERROR: "csum_partial" [fs/reiserfs/reiserfs.ko] undefined!
    make[1]: *** [__modpost] Error 1
    make: *** [modules] Error 2

This is due to a known weakness of symbol exports: if a symbol's
only in-core user is an EXPORT_SYMBOL from a lib-y section, the
symbol is not linked in.

The solution is to move the export to x8664_ksyms_64.c - but the real
solution would be to fix kbuild.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/x8664_ksyms_64.c

@@ -2,6 +2,7 @@
    All C exports should go in the respective C files. */
 
 #include <linux/module.h>
+#include <net/checksum.h>
 #include <linux/smp.h>
 
 #include <asm/processor.h>
@@ -29,6 +30,8 @@ EXPORT_SYMBOL(__copy_from_user_inatomic);
 EXPORT_SYMBOL(copy_page);
 EXPORT_SYMBOL(clear_page);
 
+EXPORT_SYMBOL(csum_partial);
+
 /*
  * Export string functions. We normally rely on gcc builtin for most of these,
  * but gcc sometimes decides not to inline them.

arch/x86/lib/csum-partial_64.c

@@ -136,8 +136,6 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
 						(__force u32)sum);
 }
 
-EXPORT_SYMBOL(csum_partial);
-
 /*
  * this routine is used for miscellaneous IP-like checksums, mainly
  * in icmp.c