When the externalsrc class is used the tasks listed in
SRCTREECOVEREDTASKS are deleted to prevent them being executed. If
externalsrc is used for the kernel then this will include
virtual/kernel:do_patch.
We can depend on do_shared_workdir instead as this will survive when
externalsrc is used.
Signed-off-by: Paul Barker <pbarker@konsulko.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>