Up to now a DragonFlyBSD developer had been maintaining his own out-of-tree patches that add support for the DragonFlyBSD target and complete ADA front-end support to all four major BSDs. A few months ago John Marino, the developer maintaining the patches, began working to mainline them to provide out-of-the-box support for C, C++, Objective-C, and Fortran.
DragonFlyBSD on GCC works fairly well and Marino noted that for some test cases DragonFly works better than FreeBSD. The back information on GCC for DragonFlyBSD can be found via this mailing list thread.
That work has been mainlined so now for next year's GCC 5.0 release there is official DragonFlyBSD operating system support.