warnings: useless semantic types

warnings: useless semantic types

* src/symtab.h (symbol_list): Represent semantic types as structure
'semantic_type'.
* src/symlist.c (symbol_list_type_new): Allocate this structure.
(symbol_list_code_props_set): Set this semantic type's status to used if it
was not declared.
* src/symtab.c (semantic_types_sorted): New.
(semantic_type_new): Set the new semantic type's location appropriately.
(symbol_check_defined): If a symbol has a type, then set this type's status
to "declared".
(semantic_type_check_defined, semantic_type_check_defined_processor): Same
as symbol_check_defined and symbol_check_defined_processor, but for semantic
types.
(symbol_check_defined): Check semantic types usefulness.
* src/symtab.h (semantic_type): New fields 'location' and 'status'.
* src/symtab.h, src/symtab.c (semantic_type_new)
(semantic_type_from_uniqstr, semantic_type_get): Accept a location as a
supplementary argument.
* tests/input.at (Unassociated types used for printer of destructor): New.
* tests/c++.at (AT_CHECK_VARIANTS): Fix an error caught by this commit.