While GCC has been around for nearly 30 years, this is the first time receiving the award from the Association for Computing Machinery. The annual award goes to "an institution or individuals that have developed a software system with lasting influence."
Four years ago is when the LLVM project captured the Programming Languages Software Award from the ACM while two years ago is when LLVM received the slightly different ACM Software System Award. Last year's winner of this award was the Coq proof assistant while those curious about the other past winners can find the listing at SIGPLAN.org.
More information on GCC receiving the 2014 Programming Languages Software Award can be found at Red Hat's RHEL blog.