kbuild: ignore cache modifiers for generating the tags files

With this patch I'm able to find the definition of _xmit_lock defined in
include/linux/netdevice.h as follows:

	struct net_device {
		...
		spinlock_t _xmit_lock ____cacheline_aligned_in_smp;
	}

Otherwise this counts as definition of ____cacheline_aligned_in_smp.
Signed-off-by: NUwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

Makefile

@@ -1378,6 +1378,7 @@ define xtags
 	if $1 --version 2>&1 | grep -iq exuberant; then \
 	    $(all-sources) | xargs $1 -a \
 		-I __initdata,__exitdata,__acquires,__releases \
+		-I __read_mostly,____cacheline_aligned,____cacheline_aligned_in_smp,____cacheline_internodealigned_in_smp \
 		-I EXPORT_SYMBOL,EXPORT_SYMBOL_GPL \
 		--extra=+f --c-kinds=+px \
 		--regex-asm='/^ENTRY\(([^)]*)\).*/\1/'; \