incus: patch lxc/rootfs directory to fix tmpfs-overlay (#477631)

  # required for go-cowsql.

  CGO_LDFLAGS_ALLOW = "(-Wl,-wrap,pthread_create)|(-Wl,-z,now)";

  # add our lxc location to incus's acceptable rootFsPaths

  # this is necessary for tmpfs/tmpfs-overlay to work

  postPatch =

    if (lib.versionAtLeast finalAttrs.version "6.16") then

      ''

        substituteInPlace internal/server/device/disk.go \

          --replace-fail '"/opt/incus/lib/lxc/rootfs/"' '"${lxc}/lib/lxc/rootfs/"'

      ''

    else

      null;

  postBuild = ''

    # build docs

    mkdir -p .sphinx/deps