I change my opinion. I'd like to leave this problem for porters.
We cannot say a certain thing about platforms which don't have PATH_MAX.
Those who want to port GLOBAL to such platforms should set PATH_MAX to
an appropriate value.
I would like to add code as follows:
Since this platform does not have PATH_MAX, you should define it
using an appropriate value for the platform.
/* #define PATH_MAX 1024 */
What do you think?