hurd: Fix build

Move PATH_MAX, NAME_MAX, IOV_MAX default definitions to the common
<isc/platform.h>.

lib/dns/gen.c

@@ -26,6 +26,8 @@
 
 #include <sys/types.h>
 
+#include <isc/platform.h>
+
 #include <ctype.h>
 #include <limits.h>
 #include <stdint.h>
@@ -142,10 +144,6 @@ static const char copyright[] =
 #define TYPECLASSFMT "%" STR(TYPECLASSLEN) "[-0-9a-z]_%d"
 #define ATTRIBUTESIZE 256
 
-#ifndef PATH_MAX
-#define PATH_MAX 1024
-#endif
-
 static struct cc {
 	struct cc *next;
 	int rdclass;