try a little harder to find APR_MAX_PATH.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@4515 d0543943-73ff-0310-b7d9-9358b9ac24b2

libs/apr/include/apr.h.in

@@ -385,6 +385,8 @@ typedef  @socklen_t_value@       apr_socklen_t;
 #define APR_PATH_MAX       PATH_MAX
 #elif defined(_POSIX_PATH_MAX)
 #define APR_PATH_MAX       _POSIX_PATH_MAX
+#elif defined(_XOPEN_PATH_MAX)
+#define APR_PATH_MAX       _XOPEN_PATH_MAX
 #else
 #error no decision has been made on APR_PATH_MAX for your platform
 #endif