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.

gdb/corelow.c

@@ -83,16 +83,16 @@ Use a core file as a target.  Specify the filename of the core file.");
 					ULONGEST *xfered_len) override;
   void files_info () override;
 
-  int thread_alive (ptid_t ptid) override;
+  bool thread_alive (ptid_t ptid) override;
   const struct target_desc *read_description () override;
 
   const char *pid_to_str (ptid_t) override;
 
   const char *thread_name (struct thread_info *) override;
 
-  int has_memory () override;
-  int has_stack () override;
-  int has_registers () override;
+  bool has_memory () override;
+  bool has_stack () override;
+  bool has_registers () override;
   bool info_proc (const char *, enum info_proc_what) override;
 };
 
@@ -922,10 +922,10 @@ core_target::xfer_partial (enum target_object object, const char *annex,
    to appear in an "info thread" command, which is quite a useful
    behaviour.
  */
-int
+bool
 core_target::thread_alive (ptid_t ptid)
 {
-  return 1;
+  return true;
 }
 
 /* Ask the current architecture what it knows about this core file.
@@ -989,19 +989,19 @@ core_target::thread_name (struct thread_info *thr)
   return NULL;
 }
 
-int
+bool
 core_target::has_memory ()
 {
   return (core_bfd != NULL);
 }
 
-int
+bool
 core_target::has_stack ()
 {
   return (core_bfd != NULL);
 }
 
-int
+bool
 core_target::has_registers ()
 {
   return (core_bfd != NULL);