[libcxx] Fix C++14 and up constexpr members in MoveOnly.

[zoecarver]

Summary

a4b8ee6 made all MoveOnly members constexpr but, some members and constructors contain expressions that are only valid in C++14 and later. This patch prefixes those methods and constructors with TEST_CONSTEXPR_CXX14.

[ldionne]

libcxx/test/support/MoveOnly.h

36–39

I think those should be OK in C++11, no? It's only a single return statement.

39

Same

[zoecarver]

libcxx/test/support/MoveOnly.h

36–39

No, unfortunately not. They both call the move constructor which isn't constexpr.

libcxx/test/support/MoveOnly.h

 class MoveOnly
 {
     MoveOnly(const MoveOnly&);
     MoveOnly& operator=(const MoveOnly&);
 
     int data_;
 public:
     constexpr MoveOnly(int data = 1) : data_(data) {}
-    constexpr MoveOnly(MoveOnly&& x)
+    TEST_CONSTEXPR_CXX14 MoveOnly(MoveOnly&& x)
         : data_(x.data_) {x.data_ = 0;}
-    constexpr MoveOnly& operator=(MoveOnly&& x)
+    TEST_CONSTEXPR_CXX14 MoveOnly& operator=(MoveOnly&& x)
         {data_ = x.data_; x.data_ = 0; return *this;}
 
     constexpr int get() const {return data_;}
 
     constexpr bool operator==(const MoveOnly& x) const {return data_ == x.data_;}
     constexpr bool operator< (const MoveOnly& x) const {return data_ <  x.data_;}
-    constexpr MoveOnly operator+(const MoveOnly& x) const { return MoveOnly{data_ + x.data_}; }
-    constexpr MoveOnly operator*(const MoveOnly& x) const { return MoveOnly{data_ * x.data_}; }
+    TEST_CONSTEXPR_CXX14 MoveOnly operator+(const MoveOnly& x) const
+        { return MoveOnly{data_ + x.data_}; }
+    TEST_CONSTEXPR_CXX14 MoveOnly operator*(const MoveOnly& x) const
+        { return MoveOnly{data_ * x.data_}; }
 };
 
 namespace std {
 
 template <>
 struct hash<MoveOnly>
 {
     typedef MoveOnly argument_type;