MFC r259100:

MFC r259100:

Pull in r196658 from upstream clang trunk:

  CodeGen: Don't emit linkage on thunks that aren't emitted because they're
  vararg.

  This can happen when we're trying to emit a thunk with available_externally
  linkage with optimization enabled but bail because it doesn't make sense for
  vararg functions.

  [LLVM] PR18098.

This should fix clang "Broken module found, compilation aborted" errors when
building the qt4-based dvbcut port.

Reported by:	se

git-svn-id: svn://svn.freebsd.org/base/stable/10@259214 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f