Index: clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -317,7 +317,11 @@
   if (StringRef(D.Dir).startswith(SysRoot)) {
     // Even if OSLibDir != "lib", this is needed for Clang in the build
     // directory (not installed) to find libc++.
-    addPathIfExists(D, D.Dir + "/../lib", Paths);
+    // Use the presence of build-specific files to detect whether we are
+    // dealing with the build tree and avoid adding 32-bit system "lib"
+    // directory otherwise.
+    if (D.getVFS().exists(D.Dir + "/../CMakeCache.txt"))
+      addPathIfExists(D, D.Dir + "/../lib", Paths);
     if (OSLibDir != "lib")
       addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
   }