Always build AthSimulation with LTO-enabled AtlasGeant4

Benjamin Morganrequested to merge
bmorgan/athena:athsim-always-lto into 24.0

Change in option default requested for mc23e in ATLASSIM-6058. No changes to build options in Athena are made, this is only for AthSimulation.

Ping @jchapman, @akraszna

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