main/check library - re-enable configure option to support forks
As clandmeter mentioned in a ticket
(https://github.com/libcheck/check/issues/138) for that project setting
the switch —disable-forks was needed to conform to the grsec kernel.
Now that this grsec/hardened kernel is gone. This change could be
reverted at some time.
At least one possible new package (testing/burp) depends on that
setting.
(from redmine: issue id 8538, created on 2018-02-21)