Switch assert(0/false) llvm_unreachable.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140367 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Phases.cpp b/lib/Driver/Phases.cpp
index f360002..d7f6ab9 100644
--- a/lib/Driver/Phases.cpp
+++ b/lib/Driver/Phases.cpp
@@ -22,6 +22,6 @@
   case Link: return "linker";
   }
 
-  assert(0 && "Invalid phase id.");
+  llvm_unreachable("Invalid phase id.");
   return 0;
 }