Gentoo's Bugzilla –
Attachment 444400 Details for
Bug 592408media-libs/mesa-12.0.1[opencl] with sys-devel/llvm-3.9.0 - src/gallium/state_trackers/clover/llvm/invocation.cpp:212:75: error: no matching function for call to clang::CompilerInvocation::setLangDefaults