Explicit locations: introduce explicit locations

Explicit locations: introduce explicit locations

This patch add support for explicit locations and switches many linespec
locations to this new location type.  This patch also converts all
linespec locations entered by the user to an explicit representation
internally (thus bypassing the linespec parser when resetting the
breakpoint).

This patch does not introduce any user-visible changes.

gdb/ChangeLog:

	* break-catch-throw.c (re_set_exception_catchpoint): Convert
	linespec into explicit location.
	* breakpoint.c (create_overlay_breakpoint)
	(create_longjmp_master_breakpoint)
	(create_std_terminate_master_breakpoint)
	(create_exception_master_breakpoint): Convert linespec into explicit
	location.
	(update_static_tracepoint): Convert linespec into explicit location.
	* linespec.c (enum offset_relative_sign, struct line_offset): Move
	location.h.
	(struct linespec) <expression, expr_pc, source_filename>
	<function_name, label_name, line_offset>: Replace with ...
	<explicit>: ... this.
	<is_linespec>: New member.
	(PARSER_EXPLICIT): New accessor macro.
	(undefined_label_error): New function.
	(source_file_not_found_error): New function.
	(linespec_parse_basic): The parser result is now an explicit location.
	Use PARSER_EXPLICIT to access it.
	Use undefined_label_error.
	(canonicalize_linespec): Convert canonical linespec into explicit
	location.
	Move string representation of location to explicit_location_to_linespec
	and use it and explicit_location_to_string to save string
	representations of the canonical location.
	(create_sals_line_offset, convert_linespec_to_sals): `ls' contains an
	explicit location.  Update all references.
	(convert_explicit_location_to_sals): New function.
	(parse_linespec): Use PARSER_EXPLICIT to access the parser
	result's explicit location.
	(linespec_state_constructor): Initialize is_linespec.
	Use PARSER_EXPLICIT.
	(linespec_parser_delete): Use PARSER_EXPLICIT to access the parser's
	result.
	(event_location_to_sals): For linespec locations, set is_linespec.
	Handle explicit locations.
	(decode_objc): 'ls' contains an explicit location now. Update all
	references.
	(symtabs_from_filename): Use source_file_not_found_error.
	* location.c (struct event_location.u) <explicit>: New member.
	(initialize_explicit_location): New function.
	(initialize_event_location): Initialize explicit locations.
	(new_explicit_location, get_explicit_location)
	(get_explicit_location_const): New functions.
	(explicit_to_string_internal): New function; most of contents moved
	from canonicalize_linespec.
	(explicit_location_to_string): New function.
	(explicit_location_to_linespec): New function.
	(copy_event_location, delete_event_location)
	(event_location_to_string_const, event_location_empty_p): Handle
	explicit locations.
	* location.h (enum offset_relative_sign, struct line_offset): Move
	here from linespec.h.
	(enum event_location_type): Add EXPLICIT_LOCATION.
	(struct explicit_location): New structure.
	(explicit_location_to_string): Declare.
	(explicit_location_to_linespec): Declare.
	(new_explicit_location, get_explicit_locationp
	(get_explicit_location_const, initialize_explicit_location): Declare.