Conditionally compile support for --enable-mapped_location.

Conditionally compile support for --enable-mapped_location.

	* decl.c (pop_label):  Handle (imperfectly) USE_MAPPED_LOCATION case.
	* decl2.c:  If USE_MAPPED_LOCATION, don't do some line number
	adjustments - which I don't understand.
	* error.c (dump_decl):  Rename "<interrnal>" to "<built-in>".
	* error.c:  Use LOCATION_FILE and EXPR_LOCATION macros.
	(print_instantiation_partial_context):  Use expand_location.
	* decl.c (duplicate_decl):  Use new DECL_IS_BUILTIN macro.
	* name-lookup.c:  Likewise.
	* lex.c (cxx_init):  Likewise.  Also use BUILTINS_LOCATION.
	* name-lookup.c:  Use input_line macro.
	* parser.c (cp_lexer_get_preprocessor_token):  Use UNKNOWN_LOCATION.
	(cp_parser_statement):  Rename locaal variable statement_locus to
	statement_location and use SET_EXPR_LOCATION macro.
	* pt.c:  Handle USE_MAPPED_LOCATION case.  Use new macros.
	* tree.c (cp_walk_subtrees):  Likewise.

From-SVN: r83923