Switch assert(0/false) llvm_unreachable.

llvm-svn: 140367
diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
index 1c49892..cd03069 100644
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -265,7 +265,7 @@
     break;
 
   default:
-    assert(0 && "Invalid #pragma pack kind.");
+    llvm_unreachable("Invalid #pragma pack kind.");
   }
 }