Use styled_string in more places

Use styled_string in more places

This adds more uses of styled_string, changing gdb to style some
output that was previously left unstyled.

gdb/ChangeLog
2019-10-01  Tom Tromey  <tom@tromey.com>

	* stack.c (print_frame, info_frame_command_core): Use
	styled_string.
	* linux-thread-db.c (try_thread_db_load_1)
	(try_thread_db_load_from_pdir_1): Use styled_string.
	* auto-load.c (file_is_auto_load_safe, execute_script_contents)
	(auto_load_section_scripts, info_auto_load_local_gdbinit)
	(maybe_print_unsupported_script_warning)
	(maybe_print_script_not_found_warning): Use styled_string.
	* ada-lang.c (user_select_syms): Use styled_string.