[libclang] Add missing CINDEX_LINKAGE from a function.

llvm-svn: 260047
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index c29a201..9284126 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -3656,8 +3656,8 @@
  * Visits the children of a cursor using the specified block.  Behaves
  * identically to clang_visitChildren() in all other respects.
  */
-unsigned clang_visitChildrenWithBlock(CXCursor parent,
-                                      CXCursorVisitorBlock block);
+CINDEX_LINKAGE unsigned clang_visitChildrenWithBlock(CXCursor parent,
+                                                    CXCursorVisitorBlock block);
 #  endif
 #endif