Make tdesc_reg string fields std::string
Make the name, group and type fields of tdesc_reg std::strings. This
way, we don't have to manually free them in ~tdesc_reg.
Doing so results in a small change in the generated tdesc. Instead of
passing an empty string for the group parameter of tdesc_create_reg, the
two modified tdesc now pass NULL. The end result should be the same.
gdb/ChangeLog:
* target-descriptions.c (struct tdesc_reg) <tdesc_reg>: Change
type of name_ parameter, adjust to std::string change.
<name, group, type>: Change type to std::string.
<~tdesc_reg>: Replace with default implementation.
<operator==>: Adjust.
(tdesc_find_register_early): Adjust.
(tdesc_register_name): Adjust.
(tdesc_register_type): Adjust.
(tdesc_register_in_reggroup_p): Adjust.
(class print_c_tdesc) <visit>: Adjust.
(class print_c_feature) <visit>: Adjust.