Fix the clang driver when "-nostdlib" is present

This patch is a fix to r252901 which changed the behavior of 
clang driver. In the presence of "-nostdlib" none of the standard
libraries should be passed to link line.

Differential Revision: http://reviews.llvm.org/D15130

llvm-svn: 254535
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 484737b..2015e3b 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -8694,8 +8694,7 @@
       if (!isAndroid)
         CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtn.o")));
     }
-  } else if (Args.hasArg(options::OPT_rtlib_EQ))
-    AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
+  }
 
   C.addCommand(llvm::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs));
 }