MXS-1328 Mark regexp functions as builtin functions

Regexp functions were not listed among the builtin read-only
functions and consequently any SELECT using one of those was
routed to master.

query_classifier/qc_sqlite/builtin_functions.c

@@ -360,6 +360,16 @@ static const char* BUILTIN_FUNCTIONS[] =
     "to_base64",
     "weight_string",
 
+    /*
+     * Regex functions
+     * https://mariadb.com/kb/en/mariadb/regular-expressions-functions/
+     */
+    "regexp",
+    "regexp_instr",
+    "regexp_replace",
+    "regexp_substr",
+    "rlike",
+
     /*
      * http://dev.mysql.com/doc/refman/5.7/en/row-subqueries.html
      */

query_classifier/test/maxscale.test

@@ -77,3 +77,5 @@ ROLLBACK TO SAVEPOINT id;
 ROLLBACK WORK TO id;
 ROLLBACK TO id;
 RELEASE SAVEPOINT id;
+
+SELECT her FROM (SELECT @@server_id as her) as t WHERE her REGEXP '.*';