This should give performance improvements to functions using this list of
tasks (sets are used for most of the other code for this reason, not sure
why this wasn't a set in the first place).
(Bitbake rev: f5daef68703481a3c243dfecc7de404e6ebfdbb6)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>