Add missing utility include, needed for std::forward

See build errors in

https://lhcb-archive.cern.ch/artifacts/nightly/lhcb-gaudi-head/1180/summaries.x86_64-slc6-gcc49-opt/Stripping/build_log.html

Approved this merge request

mentioned in commit lhcb/Stripping@2be492ca

mentioned in merge request lhcb/Stripping!24 (merged)

Approved this merge request

Milestone changed to %v28r0

Reassigned to @clemenci

Status changed to merged

mentioned in commit 73dc799a

mentioned in merge request atlas/Gaudi!60 (merged)

mentioned in commit atlas/Gaudi@60d75075

Mentioned in commit leggett/AtlasGaudi@60d75075

Mentioned in commit graven/Gaudi@73dc799a