If we don't do this, target and cross recipes end up with different sstate
checksums for shared work directory tasks which is bad in the case of gcc.
It leads to multiple fetch/unpack tasks against the shared directory
which ends up with build failures/races.
(From OE-Core rev: 793ce6cd9aa632e0f13789c8293770a86085d28d)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>