Having eglibc rebuild every time DISTRO_FEATURES changes is suboptimal.
This rewrite takes advantage of bitbake's understanding of the contains
function so this doesn't happen. The code is marginally uglier but is
worth the benefit in fewer libc rebuilds.
(From OE-Core rev: 9a272ee6d72fc727a2dfe660ceded560a9f1ae88)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>