Make exceptions use std::string and be self-managing

Make exceptions use std::string and be self-managing

This changes the exception's "message" member to be a shared_ptr
wrapping a std::string.  This allows removing the stack of exception
messages, because now exceptions will self-destruct when needed.  This
also adds a noexcept copy constructor and operator= to gdb_exception,
plus a "what" method.

gdb/ChangeLog
2019-04-08  Tom Tromey  <tom@tromey.com>

	* xml-support.c (gdb_xml_parser::parse): Update.
	* x86-linux-nat.c (x86_linux_nat_target::enable_btrace): Update.
	* value.c (show_convenience): Update.
	* unittests/cli-utils-selftests.c (test_number_or_range_parser)
	(test_parse_flags_qcs): Update.
	* thread.c (thr_try_catch_cmd): Update.
	* target.c (target_translate_tls_address): Update.
	* stack.c (print_frame_arg, read_frame_local, read_frame_arg)
	(info_frame_command_core, frame_apply_command_count): Update.
	* rust-exp.y (rust_lex_exception_test): Update.
	* riscv-tdep.c (riscv_print_one_register_info): Update.
	* remote.c (remote_target::enable_btrace): Update.
	* record-btrace.c (record_btrace_enable_warn): Update.
	* python/py-utils.c (gdbpy_convert_exception): Update.
	* printcmd.c (do_one_display, print_variable_and_value): Update.
	* mi/mi-main.c (mi_print_exception): Update.
	* mi/mi-interp.c (mi_cmd_interpreter_exec): Use SCOPE_EXIT.
	* mi/mi-cmd-stack.c (list_arg_or_local): Update.
	* linux-nat.c (linux_nat_target::attach): Update.
	* linux-fork.c (class scoped_switch_fork_info): Update.
	* infrun.c (displaced_step_prepare): Update.
	* infcall.c (call_function_by_hand_dummy): Update.
	* guile/scm-exception.c (gdbscm_scm_from_gdb_exception): Update.
	* gnu-v3-abi.c (print_one_vtable): Update.
	* frame.c (get_prev_frame_always): Update.
	* f-valprint.c (info_common_command_for_block): Update.
	* exec.c (try_open_exec_file): Update.
	* exceptions.c (print_exception, exception_print)
	(exception_fprintf, exception_print_same): Update.
	* dwarf2-frame.c (dwarf2_build_frame_info): Update.
	* dwarf-index-cache.c (index_cache::store)
	(index_cache::lookup_gdb_index): Update.
	* darwin-nat.c (maybe_cache_shell): Update.
	* cp-valprint.c (cp_print_value_fields): Update.
	* compile/compile-cplus-symbols.c (gcc_cplus_convert_symbol)
	(gcc_cplus_symbol_address): Update.
	* compile/compile-c-symbols.c (gcc_convert_symbol)
	(gcc_symbol_address, generate_c_for_for_one_variable): Update.
	* common/selftest.c: Update.
	* common/common-exceptions.h (struct gdb_exception) <message>: Now
	a std::string.
	(exception_try_scope_entry, exception_try_scope_exit): Don't
	declare.
	(struct exception_try_scope): Remove.
	(TRY): Don't use exception_try_scope.
	(struct gdb_exception): Add constructor, operator=.
	<what>: New method.
	(struct gdb_exception_RETURN_MASK_ALL)
	(struct gdb_exception_RETURN_MASK_ERROR)
	(struct gdb_exception_RETURN_MASK_QUIT): Add constructor.
	(struct gdb_quit_bad_alloc): Update.
	* common/common-exceptions.c (exception_none): Change
	initializer.
	(struct catcher) <state, exception>: Initialize inline.
	<prev>: Remove member.
	(current_catcher): Remove.
	(catchers): New global.
	(exceptions_state_mc_init): Simplify.
	(catcher_pop): Remove.
	(exceptions_state_mc, exceptions_state_mc_catch): Update.
	(try_scope_depth, exception_try_scope_entry)
	(exception_try_scope_exit): Remove.
	(throw_exception_sjlj): Update.
	(exception_messages, exception_messages_size): Remove.
	(throw_it): Simplify.
	(gdb_exception_sliced_copy): Remove.
	(throw_exception_cxx): Update.
	* cli/cli-script.c (script_from_file): Update.
	* breakpoint.c (insert_bp_location, update_breakpoint_locations):
	Update.
	* ada-valprint.c (ada_val_print): Update.
	* ada-lang.c (ada_to_fixed_type_1, ada_exception_name_addr)
	(create_excep_cond_exprs): Update.

gdb/gdbserver/ChangeLog
2019-04-08  Tom Tromey  <tom@tromey.com>

	* server.c (handle_btrace_general_set, handle_qxfer_btrace)
	(handle_qxfer_btrace_conf, detach_or_kill_for_exit_cleanup)
	(captured_main, main): Update.
	* gdbreplay.c (main): Update.