DragonEgg takes advantage of the plug-in capabilities of GCC 4.5 and later while aiming to support all of the languages supported by the GNU Compiler Collection on an unmodified GCC installation. However, those are the long-term goals and is not where DragonEgg is currently positioned. DragonEgg's C support should be spot on while the C++ support is fairly good and continuing to mature. The level of support for Fortran, ADA, Objective-C, Objective-C++, and Java all varies, but C is certainly the best supported language by this project to use LLVM as a GCC back-end.
Right now DragonEgg also requires patching GCC and is only supported on x86 and x86_64 architectures running Linux or Darwin. With all of that said, the DragonEgg developers do not yet consider this GCC plug-in as being production ready.
This release of DragonEgg 2.8 is, of course, dependent upon LLVM 2.8. Those interested in trying it out can find more on the DragonEgg page.