am 7ebce18a: am 0cad8ee2: am 572e9acc: Merge "Always use prebuilt clang, even if we\'re explicitly building clang/LLVM."

* commit '7ebce18ac0cff11fbc0877d108463a4538a33194':
  Always use prebuilt clang, even if we're explicitly building clang/LLVM.