When building with the class, avoid errors like:
"sstate found an absolute path symlink /xxx/vendor pointing at
/xxx/import/vendor. Please replace this with a relative link."
Use relative symlinks instead.
(From OE-Core rev: fc4f589cc7a8e5feba7940ccb244a74bd5f96371)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>