kbuild: escape meta characters in regular expression in make TAGS

Alexey Dobriyan <adobriyan@gmail.com> introduced a code adds
menuconfig SOMETHING in Kconfig to tags output when you did "make tags".

See http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=80ff26241623875636674a31c0540a78c0fb5433

"make tags" may work fine with his code. However make TAGS doesn't work well
because etags command requires backslashes to escape meta characters like
`(', `)' and `|'.

Here is a patch.
Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -1431,7 +1431,7 @@ define xtags
 	elif $1 --version 2>&1 | grep -iq emacs; then \
 	    $(all-sources) | xargs $1 -a; \
 	    $(all-kconfigs) | xargs $1 -a \
-		--regex='/^[ \t]*(menu|)config[ \t]+\([a-zA-Z0-9_]+\)/\2/'; \
+		--regex='/^[ \t]*\(\(menu\)*config\)[ \t]+\([a-zA-Z0-9_]+\)/\3/'; \
 	    $(all-defconfigs) | xargs -r $1 -a \
 		--regex='/^#?[ \t]?\(CONFIG_[a-zA-Z0-9_]+\)/\1/'; \
 	else \