[autoconf] Prune "runtime" stuff in configure, corresponding to r191835.

  config.status: executing runtime/Makefile commands
  autoconf/install-sh: runtime/Makefile does not exist.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194376 91177308-0d34-0410-b5e6-96231b3b80d8