Explicit locations: introduce new struct event_location-based API

Explicit locations: introduce new struct event_location-based API

This patch introduces the new breakpoint/"linespec" API based on
a new struct event_location.  This API currently only supports
traditional linespecs, maintaining the status quo of the code base.
Future patches will add additional functionality for other location
types such as address locations.

gdb/ChangeLog:

	* Makefile.in (SFILES): Add location.c.
	(HFILES_NO_SRCDIR): Add location.h.
	(COMMON_OBS): Add location.o.
	* linespec.c (linespec_lex_to_end): New function.
	* linespec.h (linespec_lex_to_end): Declare.
	* location.c: New file.
	* location.h: New file.