Ignore .dirstamp files
Ignore .dirstamp files

The autotools build system now produces .dirstamp files.

Signed-off-by: Sebastian Ramacher <63df716952f6985d63bd730444128636613d6384@debian.org>

phw/libdiscid,metabrainz/libdiscid,phw/libdiscid,metabrainz/libdiscid