Added LLVM_FALLTHROUGH to address warning: this statement may fall through. NFC.

llvm-svn: 304650
diff --git a/clang/lib/AST/NestedNameSpecifier.cpp b/clang/lib/AST/NestedNameSpecifier.cpp
index 514c7c9..e2e0dbe 100644
--- a/clang/lib/AST/NestedNameSpecifier.cpp
+++ b/clang/lib/AST/NestedNameSpecifier.cpp
@@ -290,6 +290,7 @@
   case TypeSpecWithTemplate:
     OS << "template ";
     // Fall through to print the type.
+    LLVM_FALLTHROUGH;
 
   case TypeSpec: {
     const Type *T = getAsType();