MSVC is stuck in the 80s.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140597 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang-c/Index.h b/include/clang-c/Index.h
index 6bd0286..fbeb14d 100644
--- a/include/clang-c/Index.h
+++ b/include/clang-c/Index.h
@@ -1557,9 +1557,7 @@
 /**
  * \brief Returns non-zero if \arg cursor is null.
  */
-static inline int clang_Cursor_isNull(CXCursor cursor) {
-  return clang_equalCursors(cursor, clang_getNullCursor());
-}
+int clang_Cursor_isNull(CXCursor);
 
 /**
  * \brief Compute a hash value for the given cursor.