Add per-operation permission flags.
* target.h (struct target_ops): New method to_set_permissions.
(target_set_permissions): New macro.
(target_insert_breakpoint): Change macro to function.
(target_remove_breakpoint): Ditto.
(target_stop): Ditto.
(may_write_registers): Declare.
(may_write_memory): Declare.
(may_insert_breakpoints): Declare.
(may_insert_tracepoints): Declare.
(may_insert_fast_tracepoints): Declare.
(may_stop): Declare.
* target.c (may_write_registers, may_write_registers_1): New globals.
(may_write_memory, may_write_memory_1): New globals.
(may_insert_breakpoints, may_insert_breakpoints_1): New globals.
(may_insert_tracepoints, may_insert_tracepoints_1): New globals.
(may_insert_fast_tracepoints, may_insert_fast_tracepoints_1): New
globals.
(may_stop, may_stop_1): New global.
(target_xfer_partial): Test for write permission.
(target_store_registers): Ditto.
(target_insert_breakpoint): New function.
(target_remove_breakpoint): New function.
(target_stop): New function.
(_initialize_targets): Add new set/show variables.
(set_write_memory_permission): New function.
(update_target_permissions): New function.
(set_target_permissions): New function.
(update_current_target): Default to_set_permissions.
(_initialize_targets): Use new globals and setter function.
* tracepoint.c (start_tracing): Test for permission.
* inferior.h (update_observer_mode): Declare.
* infrun.c (non_stop_1): Define earlier.
(observer_mode, observer_mode_1): New globals.
(set_observer_mode, show_observer_mode): New functions.
(update_observer_mode): New function.
(_initialize_infrun): Define "set observer" command.
* remote.c (PACKET_QAllow): New optional packet.
(remote_protocol_features): Add QAllow.
(remote_set_permissions): New function.
(remote_start_remote): Call it.
(init_remote_ops): Add it to target vector.
(_initialize_remote): Add config command for QAllow.
* gdb.texinfo (Observer Mode): New section.
(General Query Packets): Document QAllow.
* gdb.base/permissions.exp: New file.
