If you are creating an SQL query to use within Moodle, you could just use the IN keyword, exactly as you have done in the example.
Alternatively, to make it a bit more cross-DB compatible, and to make your queries run a bit faster when there is only one item in the list, you can write:
list($dsql, $dparam) = $DB->get_in_or_equal(array('2014-03-13', '2014-03-12'), SQL_PARAMS_NAMED);
$sql = "SELECT count(*) as number_of_records,
count(CASE WHEN result = 'SUCCESS' THEN 1 END) as successful_builds_no,
min(CASE WHEN result = 'FAILURE' THEN 0 ELSE 1 END) as is_success,
min(duration) as best_duration,
max(build_date) as build_date
FROM {selenium_results}
WHERE build_date $dsql
GROUP BY build_date";
$result = $DB->get_records_sql($sql, $dparams);
OR, if you just want to get all the matching records from the given table (and then worry about doing the calculations in PHP), you could write:
$result = $DB->get_records_list('selenium_results', 'build_date', array('2014-03-13', '2014-03-12'));
(I've not run any of the code above, so apologies for any typos)