Fix MSVC narrowing conversion warning.

llvm-svn: 312479
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 9adade5..8f4a908 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -2816,7 +2816,7 @@
       RecordData::value_type Record[] = {SUBMODULE_DEFINITION,
                                          ID,
                                          ParentID,
-                                         Mod->Kind,
+                                         (RecordData::value_type)Mod->Kind,
                                          Mod->IsFramework,
                                          Mod->IsExplicit,
                                          Mod->IsSystem,