test_UI_Hybrid fails with "llvm-extract: not found"

llvm-extract is not provided anymore on debian.

You either have to call /usr/lib/llvm-3.5/bin/llvm-extract which is not on the standard path, or call llvm-extract-3.5 directly.

I think the same issue happens with clang and opt. We should maybe call these tools by using LLVM_PATH + "/bin/" + toolname
