Apply r207674 from the clangbsd project branch:

Make "clang -print-multi-os-directory" return "." on amd64, matching
gcc's behaviour.  This is needed because some ports use the option to
determine the installation directory for their libraries.

Requested by:	kwm
Approved by:	rpaulo (mentor)

contrib/llvm/tools/clang/lib/Driver/Driver.cpp

@@ -470,7 +470,7 @@ bool Driver::HandleImmediateArgs(const Compilation &C) {
       break;
 
     case llvm::Triple::x86_64:
-      llvm::outs() << "x86_64" << "\n";
+      llvm::outs() << "." << "\n";
       break;
 
     case llvm::Triple::ppc64: