Make GenericDialect support from-first syntax (apache#1911)

Author: simonvandel

src/dialect/generic.rs

@@ -112,6 +112,10 @@ impl Dialect for GenericDialect {
         true
     }
 
+    fn supports_from_first_select(&self) -> bool {
+        true
+    }
+
     fn supports_asc_desc_in_column_definition(&self) -> bool {
         true
     }