Recipes which use a shared workdir (e.g. gcc-runtine and libgcc) can
race over temporary files causing interesting build failures.
Using B instead of S avoids this problem.
[YOCTO #12605]
(From OE-Core rev: d6c13a5ff441f7076eb327c0d0b747bd7603db0f)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>