Absolute path symlinks are a bit of a pain for sstate and the native versions
of these recipes currently contain broken symlinks as a result. There are
only a small number of problematic recipes, at least in OE-Core, namely the
three here.

Rather than trying to make sstate handle this magically, which turns out to
be a harder problem than you'd first realise, simply make the symlinks relative
early in the process and avoid all the problems.

The alternative is adding new complexity to sstate which we could really
do without as without the complexity, you can't always tell where the
absolute symlink is relative to (due to prefixes used for native sstate).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>