Make helpers static. No functionality change.

llvm-svn: 321425
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index dd96148..3dc961d 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -2148,7 +2148,7 @@
   return true;
 }
 
-bool isStructEmpty(QualType Ty) {
+static bool isStructEmpty(QualType Ty) {
   const RecordDecl *RD = Ty->castAs<RecordType>()->getDecl();
 
   if (!RD->field_empty())