tests: Fix build on Hurd
tests: Fix build on Hurd

As PATH_MAX is not defined on Hurd, let's check for it and define
whenever it is necessary.

https://bugs.freedesktop.org/show_bug.cgi?id=74313

ya-mouse/spice,ya-mouse/spice,fgouget/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,fgouget/spice,Fantu/spice,SPICE/spice,fgouget/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,Fantu/spice,ya-mouse/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice