The LLVM code has been merged to mainline for the Retpoline x86 mitigation technique for Spectre Variant 2. This will be back-ported to LLVM 6.0 and also LLVM 5.0 with an immediate point release expected to get this patched compiler out in the wild…

Source: Phoronix – Initial Retpoline Support Added To LLVM For Spectre v2 Mitigation