Ensure the symbol PATH_MAX is defined for illumos

--- fio-3.28/os/os-solaris.h-orig	Wed Sep  8 09:59:48 2021
+++ fio-3.28/os/os-solaris.h	Tue Nov 23 09:07:17 2021
@@ -14,6 +14,7 @@
 #include <sys/byteorder.h>
 #include <sys/statvfs.h>
 #include <pthread.h>
+#include <limits.h>
 
 #include "../file.h"
 #include "../lib/types.h"