With the X.Org Server code originating from the X Server code-base that's been under development for the past 25 years, there's lots of crufty old code still present that was written before ANSI C was even standardized. Over time, the code has gotten out of shape and doesn't comply with today's best practices.
When Keith began his clean-up there were 1047 warnings in the default X.Org Server build! But after some work and cleaning up the X.Org Server code and various external modules, he has managed to reduce the compiler warning count to zero!
Keith is going to hold off on merging the cleaned-up code until after the X.Org Server 1.15 release, which should happen before the end of the year and has many new features. The cleaned-up X.Org Server code will arrive with X.Org Server 1.16 in 2014.
Details on Keith's clean-up can be found via his blog.