Switch assert(0/false) llvm_unreachable.

llvm-svn: 140367
diff --git a/clang/lib/Analysis/PrintfFormatString.cpp b/clang/lib/Analysis/PrintfFormatString.cpp
index eb018f1..770cd37 100644
--- a/clang/lib/Analysis/PrintfFormatString.cpp
+++ b/clang/lib/Analysis/PrintfFormatString.cpp
@@ -461,7 +461,7 @@
     HasAlternativeForm = 0;
     HasPlusPrefix = 0;
   } else {
-    assert(0 && "Unexpected type");
+    llvm_unreachable("Unexpected type");
   }
 
   return true;