Prepare for the native inotify impl

[arrowd]

Summary

This is a preparation for D50315

devel/libinotify: Prepare for the native inotify impl
The idea behind the change is to leave the library as-is to allow old programs
linked to it to run, but prevent new programs from linking to it. This is
achieved by replacing libinotify sys/inotify.h with a native one and removing
LDFLAGS from the .pc file

devel/glib20: Prepare for the native inotify impl

devel/qt6-base: Prepare for the native inotify impl

[markj]

My review of ports-related things is probably not very useful, but I don't see anything too strange here.