Add missing include for windows.
Add missing include for windows.

nickerso/libcellml,cellml/libcellml,libcellml/buildbot-testing,cellml/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,libcellml/buildbot-testing,MichaelClerx/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,nickerso/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,hsorby/libcellml