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

llvm-svn: 304473
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 527d45b..4c117f5 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -4215,6 +4215,7 @@
     Diag(Result.KeywordLoc, diag::warn_microsoft_dependent_exists)
       << Result.IsIfExists;
     // Fall through to skip.
+    LLVM_FALLTHROUGH;
       
   case IEB_Skip:
     Braces.skipToEnd();