On case insensitive filesystems, "tags" and "TAGS" target will try to
overwrite the same file. Allow MinGW to use "ETAGS" instead.
These two targets do produce real files; do not put them on .PHONY target
list.
Signed-off-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>