I’m try compile UE4.5 on my Mac OS X 10.10 using Xcode 6.1, but compiling not END! I’m waited 3 hours, but it not ended. I’m also see the UE4Editor-Mac-Debug in Binaries/Mac, but its size 40.2 MB. No errors. Why? The UE4 not support OS X 10.10 and Xcode 6? Before I’m updated my MacBook to Yosemite (Mavericks 10.9.5), and my Xcode (5.1.1) UE4.4 compiled successfully.
Hi. I would rather suspect the new Clang in Xcode 6.1 to be causing some issues on your Mac 
What Mac is it, how many CPU cores and how much memory does it have? It sounds like a problem with not enough memory to run one instance of Clang compiler per CPU core.
We’re using Yosemite on many Macs at Epic (and we’ve been testing with Yosemite pre-release versions) and as far as I know, we didn’t run into this problem after update.