Import new C source of truth css-layout

fbshipit-source-id: e866918d6c62fc1cf3a04c269f782b94db9b875a

CSSLayout/CSSMacros.h

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#ifndef __CSS_MACROS_H
+#define __CSS_MACROS_H
+
+#ifdef __cplusplus
+# define CSS_EXTERN_C_BEGIN extern "C" {
+# define CSS_EXTERN_C_END   }
+#else
+# define CSS_EXTERN_C_BEGIN
+# define CSS_EXTERN_C_END
+#endif
+
+#endif