Switch assert(0/false) llvm_unreachable.

llvm-svn: 140367
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index f1c6d12..7380401 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -1585,7 +1585,7 @@
   // TODO: Build AST.
 
   switch (T) {
-  default: assert(0 && "Not a builtin primary expression!");
+  default: llvm_unreachable("Not a builtin primary expression!");
   case tok::kw___builtin_va_arg: {
     ExprResult Expr(ParseAssignmentExpression());