The problem is due to "webkit/Source/WTF/wtf/threads/Signals.cpp:33:10: fatal error: 'MachExceptionsServer.h' file not found"
Yeah, the solution to this is to run the mig stuff from PlatformMac.cmake if we are on a Mach platform. idk if we have any mach ports other than Darwin so maybe that's just if(APPLE).