Class-ify lm_info_aix

Class-ify lm_info_aix

This patch makes lm_info_aix a "real" class.  It uses std::string,
initializes fields in-class and replaces XCNEW/xfree with new/delete.
The solib_aix_new_lm_info can be replaced by using the default copy
constructor.

gdb/ChangeLog:

	* solib-aix.c (struct lm_info_aix): Initialize fields in-class.
	<filename, member_name>: Change type to std::string.
	(solib_aix_new_lm_info, solib_aix_xfree_lm_info): Remove.
	(library_list_start_library): Allocate lm_info_aix with new.
	(solib_aix_free_library_list, solib_aix_free_so): Free with delete.
	(solib_aix_current_sos): Adapt to std::string, copy lm_info_aix
	with copy constructor.