This patch is libgc for core-updates.

On GNU/Hurd systems during the 'Check' phase, there is a deadlock  
caused by the 'gctest' test.

We set "--disable-gcj-support" to configure script to pass the 'gctest'  
test.

bug report:
https://lists.opendylan.org/pipermail/bdwgc/2017-April/006275.html
discussion:
https://lists.gnu.org/archive/html/bug-hurd/2017-01/msg00008.html

Tested in Linux-x86_64, Hurd and cross-compiling (master branch).