pv-wrap: Use correct bwrap exports while using an interpreter
The Flatpak code that deals with X11, D-Bus etc... searches in both the real root filesystem and also the FEX-Emu rootfs.
But because bwrap's mount(2) doesn't do an automatic remap of the paths, a workaround was manually implemented. Every time a file/directory was available in the interpreter root, we adjusted the bind to use the FEX-Emu's rootfs.
However this introduced an issue where the /run/host/...
bind mounts
would point to the FEX-Emu rootfs overlay instead of the the real host,
as we would normally expect.
To fix that we need to always keep the binds as-is, unless the real host
root doesn't have the file we are trying to bind. And only in that case
we should switch to the interpreter rootfs.
Helps #98 (closed)