Define _KMEMUSER before including BSD kernel headers.

Recent versions of NetBSD hide certain kernel structures needed by the
KVM target from userland unless this macro is defined.

gdb/ChangeLog:

	* bsd-kvm.o: Define _KMEMUSER.
	* configure.ac: Define _KMEMUSER when checking for "struct lwp".
	* configure: Regenerate.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2017-09-04  John Baldwin  <jhb@FreeBSD.org>
+
+	* bsd-kvm.o: Define _KMEMUSER.
+	* configure.ac: Define _KMEMUSER when checking for "struct lwp".
+	* configure: Regenerate.
+
 2017-09-04  John Baldwin  <jhb@FreeBSD.org>
 
 	* amd64-fbsd-nat.c: Add include of "x86-xstate.h".

gdb/bsd-kvm.c

@@ -17,6 +17,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#define _KMEMUSER
 #include "defs.h"
 #include "cli/cli-cmds.h"
 #include "command.h"

gdb/configure

@@ -13571,6 +13571,7 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/param.h>
+#define _KMEMUSER
 #include <sys/lwp.h>
 int
 main ()

gdb/configure.ac

@@ -1434,6 +1434,7 @@ AC_CHECK_MEMBERS([struct thread.td_pcb], [], [],
 # See if <sys/lwp.h> defines `struct lwp`.
 AC_CACHE_CHECK([for struct lwp], gdb_cv_struct_lwp,
 [AC_TRY_COMPILE([#include <sys/param.h>
+#define _KMEMUSER
 #include <sys/lwp.h>], [struct lwp l;],
 gdb_cv_struct_lwp=yes, gdb_cv_struct_lwp=no)])
 if test $gdb_cv_struct_lwp = yes; then