Index: lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- lib/Driver/ToolChains/Gnu.cpp
+++ lib/Driver/ToolChains/Gnu.cpp
@@ -1670,6 +1670,15 @@
       GCCToolchainDir = GCCToolchainDir.drop_back(); // remove the /
 
     Prefixes.push_back(GCCToolchainDir);
+
+    // If we have a SysRoot, try that too as GCCToolchainDir may not
+    // have support for the target.  This can happen, for example, if
+    // clang was configured with -DGCC_INSTALL_PREFIX and we run
+    // regression tests with --sysroot.
+    if (!D.SysRoot.empty()) {
+      Prefixes.push_back(D.SysRoot);
+      AddDefaultGCCPrefixes(TargetTriple, Prefixes, D.SysRoot);
+    }
   } else {
     // If we have a SysRoot, try that first.
     if (!D.SysRoot.empty()) {