Going back years there's been a port of Intel's Cilk Plus multi-threading support to GCC but it hasn't been quick to reach master. Only last month was it approved by the GCC steering committee that the Cilk Plus run-time library can be merged.
As of last week, the _Cilk_spawn and _Cilk_sync keywords were committed followed immediately by the libcilkrts run-time library. There were also a few other GNU Compiler Collection commits concerning the Cilk Plus enablement.
Cilk Plus is an extension of C and C++ to offer easy yet powerful multi-core / vector processing programming. There's three Cilk Plus keywords to make parallel programming easier and efficient. More details on Cilk Plus, which can now be exploited by GCC, can be found via Wikipedia.
Up to now there's been only official support for Cilk Plus parallel programming within Intel's C++ Compiler but LLVM's Clang has also been working on a yet-to-be-merged implementation. It's great to see this OpenMP alternative being yet another feature for the GCC 4.9 compiler release that will likely premiere in H1'2014.