This will allow to connect with services being put in place by distros such as
Fedora, where one can retrieve DSOs by their build-id.

Example usage:

	for buildid in $(perf buildid-cache --missing perf.data | cut -d' ' -f1) ; do
		echo "trying to get $buildid"
		wget -q https://darkserver.fedoraproject.org/buildids/$buildid
		cat $buildid ; echo
		rm -f $buildid
	done

Now its just a matter of some porcelain to get the details provided by such a
service, retrieve the file and use 'perf buildid-cache --add $FILE' to insert
it in the cache, then use 'perf report' or 'annotate' that will find the
required files in the cache.

More information about the darkserver service at:

	https://darkserver.fedoraproject.org/

Cc: David Ahern <dsahern@gmail.com>
Cc: Frank Eigler <fche@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kushal Das <kdas@redhat.com>
Cc: Mark Wielaard <mjw@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-6fuktuiyjn4jykxmt7c9f7xq@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>