Fixes#838.
xattrs were historically disabled in 2017, since then, NFS v4.2 gained
support for xattrs and almost all filesystems support xattrs. In
addition, moving the build directory to a xattrs-supporting filesystem
is always an option. Programs may exploit xattrs (including ACLs) during
their build process and testing phase, to better serve these programs,
we will remove this limitation.
Lix will use POSIX ACLs for its UNIX domain sockets in the future and be
one of these programs which will run tests making use of xattrs, while
not writing any xattrs in the derivation outputs themselves.
xattrs are still scrubbed from derivation outputs so it is not possible
to obtain an advantage by writing a security-related xattr to a well
chosen file.
Tests were added to test these scenarios on Linux. Darwin is carefully
excluded because of #1008 and #1090, solving that is welcome. In the
meantime, they are marked xfail.
Change-Id: Ia3255eeb8442e83db4f10dcb5a51cbc368a2550d
Signed-off-by: Raito Bezarius <raito@lix.systems>
