x86: export native_read_tsc

native_read_tsc is needed by modules, so it should be exported.

make -C /home/jeremy/hg/xen/paravirt/linux O=/home/jeremy/hg/xen/paravirt/linux-x86_64
Using /home/jeremy/hg/xen/paravirt/linux as source for kernel

 GEN     /home/jeremy/hg/xen/paravirt/linux-x86_64/Makefile
 CHK     include/linux/version.h
 CHK     include/linux/utsrelease.h
 CALL    /home/jeremy/hg/xen/paravirt/linux/scripts/checksyscalls.sh
 CHK     include/linux/compile.h

Kernel: arch/x86/boot/bzImage is ready (#49)
Building modules, stage 2.
MODPOST 257 modules
ERROR: "native_read_tsc" [drivers/input/gameport/gameport.ko] undefined!

---
arch/x86/kernel/rtc.c | 2 +-

1 file changed, 1 insertion(+), 1 deletion(-)

===================================================================

@@ -204,4 +204,4 @@ unsigned long long native_read_tsc(void)
 

	return EAX_EDX_VAL(val, low, high);
}

-
+EXPORT_SYMBOL(native_read_tsc);