glibc 2.28 slightly changed the behaviour of sigaddset() which broke
multiprocessing. Backport a patch from Python 3.6 to solve this.
(From OE-Core rev: df1874eda517070dab86270ffafd5fe9a307e76b)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
