Class-ify lm_info_target
This patch makes lm_info_target a "real" class. It adds a destructor,
uses std::string, initializes the fields and replaces XCNEW/xfree with
new/delete.
gdb/ChangeLog:
* solib-target.c (struct lm_info_target): Add destructor,
initialize fields.
<name>: Change type to std::string.
(library_list_start_library): Allocate lm_info_target with new.
(solib_target_free_library_list): Free lm_info_target with
delete.
(solib_target_current_sos): Adapt to std::string.
(solib_target_free_so): Free lm_info_target with delete.