CMake previously generated Xcode project files labeled as 2.4-compatible
by recent versions of Xcode (3.0 and 3.1).  It is better to generate
native Xcode 3.0 and 3.1 projects.  In particular, this can improve
build times by using the "Build independent targets in parallel"
feature.

Patch from Doug Gregor.  See issue #9216.