[libcxx][test] {move,reverse}_iterator cannot be instantiated for a type with no operator*

Since their nested reference types are defined in terms of `iter_reference_t<T>`, which examines `decltype(*declval<T>())`.

Differential Revision: https://reviews.llvm.org/D117371

Author: CaseyCarter

libcxx/test/std/iterators/predef.iterators/move.iterators/move.iter.ops/move.iter.op=/move_iterator.pass.cpp

@@ -42,7 +42,7 @@ struct ToIter {
     typedef char *pointer;
     typedef char &reference;
     typedef char value_type;
-    typedef value_type difference_type;
+    typedef signed char difference_type;
 
     explicit TEST_CONSTEXPR_CXX17 ToIter() : m_value(0) {}
     TEST_CONSTEXPR_CXX17 ToIter(const ToIter &src) : m_value(src.m_value) {}
@@ -57,6 +57,8 @@ struct ToIter {
         return *this;
     }
     char *m_value;
+
+    reference operator*() const;
 };
 
 TEST_CONSTEXPR_CXX17 bool test_conv_assign()

libcxx/test/std/iterators/predef.iterators/reverse.iterators/reverse.iter.cmp/three-way.pass.cpp

@@ -42,6 +42,8 @@ struct Iter {
 
     constexpr Iter(double value): m_value(value) {}
     double m_value;
+
+    reference operator*() const;
 private:
     friend constexpr bool operator==(const Iter& l, const Iter& r) = default;
     friend constexpr std::partial_ordering operator<=>(const Iter& l, const Iter& r) = default;
@@ -57,6 +59,8 @@ struct ConstIter {
     constexpr ConstIter(double value): m_value(value) {}
     constexpr ConstIter(Iter it): m_value(it.m_value) {}
     double m_value;
+
+    reference operator*() const;
 private:
     friend constexpr bool operator==(const ConstIter& l, const ConstIter& r) = default;
     friend constexpr std::partial_ordering operator<=>(const ConstIter& l, const ConstIter& r) = default;

libcxx/test/std/iterators/predef.iterators/reverse.iterators/reverse.iter.cons/assign.pass.cpp

@@ -51,6 +51,8 @@ struct ToIter {
         return *this;
     }
     char *m_value;
+
+    reference operator*() const;
 };
 
 TEST_CONSTEXPR_CXX17 bool tests() {