G M:  Make valarray a little more forgiving to compilers not quite so gifted.  This has no impact on clang.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@190731 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/valarray b/include/valarray
index d4e9015..5113516 100644
--- a/include/valarray
+++ b/include/valarray
@@ -2628,7 +2628,7 @@
 };
 
 template<class _ValExpr>
-__val_expr<_ValExpr>::operator valarray<result_type>() const
+__val_expr<_ValExpr>::operator valarray<__val_expr::result_type>() const
 {
     valarray<result_type> __r;
     size_t __n = __expr_.size();