hurd: Fix getting VM_MIN/MAX_ADDRESS

gnu-nat.c was getting the inclusion of vm_param.h only by luck. We need
to explicitly include it to be sure to get the definitions of
VM_MIN/MAX_ADDRESS.

gdb/ChangeLog:

	* gnu-nat.c: Include <mach/vm_param.h>.

gdb/gnu-nat.c

@@ -32,6 +32,7 @@ extern "C"
 #include <mach/message.h>
 #include <mach/notify.h>
 #include <mach/vm_attributes.h>
+#include <mach/vm_param.h>
 
 #include <hurd.h>
 #include <hurd/interrupt.h>