Add a missing include for clang.


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56118 75b3775d-3801-0410-9e12-e2e43121521d
Add a missing include for clang.

git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56119 75b3775d-3801-0410-9e12-e2e43121521d