  Monte Carlo simulation results are reported on magnetic ordering in ABC
stacked Kagom\'{e} layers with fcc symmetry for both XY and Heisenberg models
which include exchange interactions with the eight near-neighbors. Well known
degeneracies of the 2D system persist in the 3D case and analysis of the
numerical data provides strong evidence for a fluctuation-driven first-order
transition to well-defined long-range order characterized as the layered $q=0$
(120-degree) spin structure. Effects of varying the inter-layer coupling are
also examined. The results are relevant to understanding the role of
frustration in IrMn$_3$ alloys widely used by the magnetic storage industry as
thin-films in the antiferromagnetic pinning layer in GMR and TMR spin valves.
Despite the technological importance of this structure, it has not previously
been noted that the magnetic Mn-ions of fcc IrMn$_3$ form Kagom\'{e} layers.
