This implement branch prediction macros likely() and unlikely() like in
Linux. When using these macros please ensure that when you use them the
condition in the branch really is very, very likely or unlikely. Think
90+% of the time. Primarily useful for error checking. (And I implement
these macros for all our error checking macros now)
See this article for more information:
https://kernelnewbies.org/FAQ/LikelyUnlikely
There are more places where these macros may make sense in renderer and
physics engine. Placing them will come in another commit down the line.
22358babda