Assume that PT_LWPINFO is always defined on FreeBSD hosts.

FreeBSD kernels have included support for this since 5.0 release.
The most recent release without support is 4.11 which was released
in January of 2005.

gdb/ChangeLog:

	* fbsd-nat.c: Assume PT_LWPINFO is always defined.
	* fbsd-nat.h: Likewise.

gdb/fbsd-nat.c

@@ -831,7 +831,6 @@ fbsd_nat_target::xfer_partial (enum target_object object,
     }
 }
 
-#ifdef PT_LWPINFO
 static bool debug_fbsd_lwp;
 static bool debug_fbsd_nat;
 
@@ -1667,7 +1666,6 @@ fbsd_nat_target::set_syscall_catchpoint (int pid, bool needed,
   return 0;
 }
 #endif
-#endif
 
 bool
 fbsd_nat_target::supports_multi_process ()
@@ -1679,7 +1677,6 @@ void _initialize_fbsd_nat ();
 void
 _initialize_fbsd_nat ()
 {
-#ifdef PT_LWPINFO
   add_setshow_boolean_cmd ("fbsd-lwp", class_maintenance,
 			   &debug_fbsd_lwp, _("\
 Set debugging of FreeBSD lwp module."), _("\
@@ -1696,5 +1693,4 @@ Enables printf debugging output."),
 			   NULL,
 			   &show_fbsd_nat_debug,
 			   &setdebuglist, &showdebuglist);
-#endif
 }