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

llvm-svn: 304479
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index d147ab0..b1fbb20 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -203,6 +203,7 @@
     }
 
     // Fall through
+    LLVM_FALLTHROUGH;
   }
 
   default: {