Suppress -Wswitch to unbreak the build.

This may need to be fixed more intelligently - I don't have enough context to
be sure what the appropriate fix is right now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175902 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index 563cc51..36224a8 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -4457,6 +4457,7 @@
 
   // Declaration kinds that don't make any sense here, but are
   // nonetheless harmless.
+  case Decl::Empty:
   case Decl::TranslationUnit:
     break;