Change `minimal_symbols' to std::vector in linespec.c structures

Change `minimal_symbols' to std::vector in linespec.c structures

This patch converts linespec.c's linespec.label_symbols member from a
VEC to a std::vector.

gdb/ChangeLog:

	* linespec.c (struct linespec) <minimal_symbols>: Change type to
	std::vector.  Update all users.
	(convert_linespec_to_sals): Use std::sort to sort minimal symbols.
	(struct collect_info) <minimal_symbols>: Likewise.
	(compare_msymbols): Return bool.  Change parameters to const
	bound_minimal_symbol references.
	(find_method, find_function_symbols, find_linespec_symbols): Change
	`minsyms' parameter to std::vector.  Update all callers.