Index: cfe/trunk/lib/Headers/CMakeLists.txt
===================================================================
--- cfe/trunk/lib/Headers/CMakeLists.txt
+++ cfe/trunk/lib/Headers/CMakeLists.txt
@@ -46,6 +46,7 @@
   tgmath.h
   tmmintrin.h
   varargs.h
+  vadefs.h
   wmmintrin.h
   __wmmintrin_aes.h
   __wmmintrin_pclmul.h
Index: cfe/trunk/lib/Headers/vadefs.h
===================================================================
--- cfe/trunk/lib/Headers/vadefs.h
+++ cfe/trunk/lib/Headers/vadefs.h
@@ -0,0 +1,50 @@
+/* ===-------- vadefs.h ---------------------------------------------------===
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *===-----------------------------------------------------------------------===
+ */
+
+/* Only include this if we are aiming for MSVC compatibility. */
+#ifndef _MSC_VER
+#include_next <vadefs.h>
+#else
+
+#ifndef __clang_vadefs_h
+#define __clang_vadefs_h
+
+#include_next <vadefs.h>
+
+/* Override macros from vadefs.h with definitions that work with Clang. */
+#ifdef _crt_va_start
+#undef _crt_va_start
+#endif
+#ifdef _crt_va_end
+#undef _crt_va_end
+#endif
+#ifdef _crt_va_arg
+#undef _crt_va_arg
+#endif
+
+#define _crt_va_start(ap, param) __builtin_va_start(ap, param)
+#define _crt_va_end(ap)          __builtin_va_end(ap)
+#define _crt_va_arg(ap, type)    __builtin_va_arg(ap, type)
+
+#endif
+#endif