PR c++/12750

	PR c++/12750
	* linespec.c (get_search_block): New function.
	(find_methods): Add FILE_SYMTATB parameter and use it and
	get_search_block to pass an appropriate block to
	lookup_symbol_in_namespace.
	(decode_line_1): Record if *ARGPTR is single-quote enclosed.
	Check if *ARGPTR starts with a filename first.
	If it does, call locate_first_half again to locate the next
	"first half" of the linespec.
	Pass FILE_SYMTATB to decode_objc and decode_compound.
	Swallow the trailing single-quote if IS_SQUOTE_ENCLOSED.
	(locate_first_half): Stop on the first colon seen.
	(decode_compound): Add FILE_SYMTAB parameter.
	Pass FILE_SYMTAB to lookup_prefix_sym and find_method.
	(lookup_prefix_sym): Add FILE_SYMTAB parameter and use
	get_search_block with lookup_symbol.
	(find_method): Add FILE_SYMTAB parameter and pass it to
	find_methods.
	(decode_objc): Use get_search_block.