Switch assert(0/false) llvm_unreachable.

llvm-svn: 140367
diff --git a/clang/lib/Driver/Action.cpp b/clang/lib/Driver/Action.cpp
index ac95446..65faa4e 100644
--- a/clang/lib/Driver/Action.cpp
+++ b/clang/lib/Driver/Action.cpp
@@ -34,7 +34,7 @@
   case VerifyJobClass: return "verify";
   }
 
-  assert(0 && "invalid class");
+  llvm_unreachable("invalid class");
   return 0;
 }