Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -648,6 +648,8 @@
   switch (Type) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    // libc++ may be installed per arch.
+    addArchSpecificRPath(*this, Args, CmdArgs);
     break;
 
   case ToolChain::CST_Libstdcxx: