fix lookup of bits/c++config.h on mingw, patch by Ismail Donmez!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112969 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/InitHeaderSearch.cpp b/lib/Frontend/InitHeaderSearch.cpp
index 3af2adb..df91713 100644
--- a/lib/Frontend/InitHeaderSearch.cpp
+++ b/lib/Frontend/InitHeaderSearch.cpp
@@ -195,6 +195,8 @@
           System, true, false, false);
   AddPath(Base + "/" + Arch + "/" + Version + "/include/c++",
           System, true, false, false);
+  AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/" + Arch,
+          System, true, false, false);
   AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/backward",
           System, true, false, false);
 }