Depending on the kernel and coreutils version, mv operations test for existence
of files and can potentially race. It also leads to the file always changing which
leads to potential problems if using and NFS share and there are other readers.
Using ln instead means we don't overwrite the file if it already exists meaning
other readers aren't disrupted and should work more reliably on NFS which is used
for sstate on the autobuilder.
Since we're not overwriting files, touch the file to show activity as would have
been done it it were reused from sstate.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
