The RadeonSI Gallium3D driver has provided OpenGL 3.3 support since Mesa 10.1 release, along with the R600 Gallium3D driver. The RadeonSI driver is what supports AMD's Radeon HD 7000 series GPUs and newer on Linux via the open-source driver. But besides needing the newer Mesa code for the OpenGL 3.3 support with the newest AMD graphics processors, the LLVM 3.5 compiler infrastructure is needed for the updated AMD GPU LLVM back-end.
David Airlie of Red Hat has now backported the necessary patches from LLVM 3.5 into Fedora's Rawhide LLVM packages and rebuilt Mesa against this patched verison of LLVM. As David wrote on his personal blog, OpenGL 3.3 support should be working for those using these Fedora Rawhide packages.
While Fedora 20 is receiving updated Mesa versions, it likely won't receive this same treatment due to the LLVM requirement. With other parts of the Fedora infrastructure depending upon LLVM, it's unlikely this work will be back-ported to the mainline LLVM package in F20. David or others though might provide a third-party Copr repository with an updated Mesa+LLVM configuration for users of this open-source Radeon driver.
RadeonSI has improved a lot recently so it's great to see desktop Linux distributions more quickly shipping new Mesa code so that it's accessible to more Linux users, including Ubuntu 14.04 LTS even using Mesa 10.2-devel.