Add datalog infrastructure for min aggregation function

This patch adds an instruction to the datalog interpreter and
constructs a new AST node for min aggregation functions.

The compiler is currently still work in progress and depends on
changes made to the handling of simple joins and the preprocessor.

Signed-off-by: Alex Horn <t-alexh@microsoft.com>

src/muz/rel/dl_relation_manager.cpp

@@ -1021,6 +1021,11 @@ namespace datalog {
         return res;
     }
 
+    table_min_fn * relation_manager::mk_min_fn(const table_base & t,
+        unsigned_vector & group_by_cols, const unsigned col)
+    {
+        return t.get_plugin().mk_min_fn(t, group_by_cols, col);
+    }
 
     class relation_manager::auxiliary_table_transformer_fn {
         table_fact m_row;