buildenv/1.3.x/osx: migrate 1.2.x/osx build env's ZeroC Ice build fix into 1.3.x.
buildenv/1.3.x/osx: migrate 1.2.x/osx build env's ZeroC Ice build fix into 1.3.x.

ccpgames/mumble-releng,ccpgames/mumble-releng