Fix MSVC "not all control paths return a value" warning

Add unreachable after enum switch statement

llvm-svn: 285390
diff --git a/clang/lib/Driver/Action.cpp b/clang/lib/Driver/Action.cpp
index 4e0c224..85e466a 100644
--- a/clang/lib/Driver/Action.cpp
+++ b/clang/lib/Driver/Action.cpp
@@ -146,6 +146,8 @@
 
     // TODO: Add other programming models here.
   }
+
+  llvm_unreachable("invalid offload kind");
 }
 
 void InputAction::anchor() {}