target_ops: Use bool throughout

target_ops: Use bool throughout

After the previous target_ops/C++ patches are all squashed and merged,
this one can go in separately.

This patch adjusts all the target methods to return bool instead of int
when they're returning a boolean.

gdb/ChangeLog:
2018-05-02  Pedro Alves  <palves@redhat.com>

	* target.h (target_ops)
	<stopped_by_sw_breakpoint, supports_stopped_by_sw_breakpoint,
	stopped_by_hw_breakpoint, supports_stopped_by_hw_breakpoint,
	stopped_by_watchpoint, have_continuable_watchpoint,
	stopped_data_address, watchpoint_addr_within_range,
	can_accel_watchpoint_condition, can_run, thread_alive,
	has_all_memory, has_memory, has_stack, has_registers,
	has_execution, can_async_p, is_async_p, supports_non_stop,
	always_non_stop_p, can_execute_reverse, supports_multi_process,
	supports_enable_disable_tracepoint,
	supports_disable_randomization, supports_string_tracing,
	supports_evaluation_of_breakpoint_conditions,
	can_run_breakpoint_commands, filesystem_is_local,
	can_download_tracepoint, get_trace_state_variable_value,
	set_trace_notes, get_tib_address, use_agent, can_use_agent,
	record_is_replaying, record_will_replay,
	augmented_libraries_svr4_read>: Adjust to return bool.
	* aarch64-linux-nat.c: All implementations adjusted.
	* aix-thread.c: All implementations adjusted.
	* arm-linux-nat.c: All implementations adjusted.
	* breakpoint.c: All implementations adjusted.
	* bsd-kvm.c: All implementations adjusted.
	* bsd-uthread.c: All implementations adjusted.
	* corelow.c: All implementations adjusted.
	* ctf.c: All implementations adjusted.
	* darwin-nat.c: All implementations adjusted.
	* darwin-nat.h: All implementations adjusted.
	* exec.c: All implementations adjusted.
	* fbsd-nat.c: All implementations adjusted.
	* fbsd-nat.h: All implementations adjusted.
	* gnu-nat.c: All implementations adjusted.
	* gnu-nat.h: All implementations adjusted.
	* go32-nat.c: All implementations adjusted.
	* ia64-linux-nat.c: All implementations adjusted.
	* inf-child.c: All implementations adjusted.
	* inf-child.h: All implementations adjusted.
	* inf-ptrace.c: All implementations adjusted.
	* inf-ptrace.h: All implementations adjusted.
	* linux-nat.c: All implementations adjusted.
	* linux-nat.h: All implementations adjusted.
	* mips-linux-nat.c: All implementations adjusted.
	* nto-procfs.c: All implementations adjusted.
	* ppc-linux-nat.c: All implementations adjusted.
	* procfs.c: All implementations adjusted.
	* ravenscar-thread.c: All implementations adjusted.
	* record-btrace.c: All implementations adjusted.
	* record-full.c: All implementations adjusted.
	* remote-sim.c: All implementations adjusted.
	* remote.c: All implementations adjusted.
	* s390-linux-nat.c: All implementations adjusted.
	* sol-thread.c: All implementations adjusted.
	* spu-multiarch.c: All implementations adjusted.
	* target-delegates.c: All implementations adjusted.
	* target.c: All implementations adjusted.
	* target.h: All implementations adjusted.
	* tracefile-tfile.c: All implementations adjusted.
	* tracefile.c: All implementations adjusted.
	* tracefile.h: All implementations adjusted.
	* windows-nat.c: All implementations adjusted.
	* x86-linux-nat.h: All implementations adjusted.
	* x86-nat.h: All implementations adjusted.