Fix PATH_MAX undeclared issue on hurd-i386 platform
Fix PATH_MAX undeclared issue on hurd-i386 platform

PATH_MAX is not defined in some platforms, most notably GNU/Hurd. Therefore, I
define the value of PATH_MAX here to 4096 which is the same value in limits.h.

irtimmer/tpm2-pk11,irtimmer/tpm2-pk11