[C++]: added platform conditionals to top level cmake in prep for more windows build eventually.
[C++]: added platform conditionals to top level cmake in prep for more windows build eventually.

galderz/Aeron,UIKit0/Aeron,RussellWilby/Aeron,ycaihua/Aeron,qed-/Aeron,gkamal/Aeron,jessefugitt/Aeron,qed-/Aeron,galderz/Aeron,mikeb01/Aeron,galderz/Aeron,oleksiyp/Aeron,lennartj/Aeron,tbrooks8/Aeron,ycaihua/Aeron,UIKit0/Aeron,buybackoff/Aeron,galderz/Aeron,buybackoff/Aeron,jerrinot/Aeron,real-logic/Aeron,strangelydim/Aeron,EvilMcJerkface/Aeron,jessefugitt/Aeron,mikeb01/Aeron,rlankenau/Aeron,tbrooks8/Aeron,ycaihua/Aeron,buybackoff/Aeron,rlankenau/Aeron,lennartj/Aeron,gkamal/Aeron,oleksiyp/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,rlankenau/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,qed-/Aeron,strangelydim/Aeron,EvilMcJerkface/Aeron,mikeb01/Aeron,gkamal/Aeron,jerrinot/Aeron,johnpr01/Aeron,jessefugitt/Aeron,qed-/Aeron,tbrooks8/Aeron,oleksiyp/Aeron,johnpr01/Aeron,RussellWilby/Aeron,strangelydim/Aeron,UIKit0/Aeron,RussellWilby/Aeron,jerrinot/Aeron,mikeb01/Aeron,real-logic/Aeron,johnpr01/Aeron,lennartj/Aeron