LWG4291 explicit map(const Allocator&) should be constexpr

Author: eisenwave

source/containers.tex

@@ -11568,7 +11568,7 @@
                     const Allocator& = Allocator());
     constexpr map(const map& x);
     constexpr map(map&& x);
-    explicit map(const Allocator&);
+    constexpr explicit map(const Allocator&);
     constexpr map(const map&, const type_identity_t<Allocator>&);
     constexpr map(map&&, const type_identity_t<Allocator>&);
     constexpr map(initializer_list<value_type>, const Compare& = Compare(),