Placate MSVC's narrowing conversion unhappiness.

llvm-svn: 301285
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 5758ac9..84d2420 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -2697,7 +2697,7 @@
   RecordData::value_type Record[] = {
       getNumberOfModules(WritingModule),
       FirstSubmoduleID - NUM_PREDEF_SUBMODULE_IDS,
-      WritingModule->Kind};
+      (unsigned)WritingModule->Kind};
   Stream.EmitRecord(SUBMODULE_METADATA, Record);
   
   // Write all of the submodules.