cpp/python: export empty and universe constructors for maps

These functions are documented and commonly used when constructing isl
maps. Export them for basic maps, maps, and union maps:

	isl_basic_map_empty
	isl_basic_map_universe

	isl_map_empty
	isl_map_universe

	isl_union_map_empty

As the arguments of these constructors do not always uniquely identify
the constructed object, named constructors are introduced.

Signed-off-by: Tobias Grosser <tobias@grosser.es>
Reviewed-by: Oleksandr Zinenko <oleksandr.zinenko@inria.fr>

include/isl/map.h

@@ -119,7 +119,9 @@ __isl_give isl_basic_map *isl_basic_map_less_at(__isl_take isl_space *dim,
 	unsigned pos);
 __isl_give isl_basic_map *isl_basic_map_more_at(__isl_take isl_space *dim,
 	unsigned pos);
+__isl_export
 __isl_give isl_basic_map *isl_basic_map_empty(__isl_take isl_space *dim);
+__isl_export
 __isl_give isl_basic_map *isl_basic_map_universe(__isl_take isl_space *dim);
 __isl_give isl_basic_map *isl_basic_map_nat_universe(__isl_take isl_space *dim);
 __isl_give isl_basic_map *isl_basic_map_remove_redundancies(
@@ -281,8 +283,10 @@ isl_bool isl_basic_map_is_subset(__isl_keep isl_basic_map *bmap1,
 isl_bool isl_basic_map_is_strict_subset(__isl_keep isl_basic_map *bmap1,
 		__isl_keep isl_basic_map *bmap2);
 
+__isl_export
 __isl_give isl_map *isl_map_universe(__isl_take isl_space *dim);
 __isl_give isl_map *isl_map_nat_universe(__isl_take isl_space *dim);
+__isl_export
 __isl_give isl_map *isl_map_empty(__isl_take isl_space *dim);
 __isl_give isl_map *isl_map_identity(__isl_take isl_space *dim);
 __isl_give isl_map *isl_map_lex_lt_first(__isl_take isl_space *dim, unsigned n);

include/isl/union_map.h

@@ -24,6 +24,7 @@ __isl_give isl_union_map *isl_union_map_from_basic_map(
 	__isl_take isl_basic_map *bmap);
 __isl_constructor
 __isl_give isl_union_map *isl_union_map_from_map(__isl_take isl_map *map);
+__isl_export
 __isl_give isl_union_map *isl_union_map_empty(__isl_take isl_space *dim);
 __isl_give isl_union_map *isl_union_map_copy(__isl_keep isl_union_map *umap);
 __isl_null isl_union_map *isl_union_map_free(__isl_take isl_union_map *umap);