package/uclibc: add upstream patch to fix build issue with gcc7

As reported on the mailing list [1], there is a build issue with gcc 7
and uClibc-ng.

Thanks to Waldemar for the fix :)

[1] http://lists.busybox.net/pipermail/buildroot/2017-May/191140.html



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>