[libc++] Give MoveOnly all six comparison operators, not just == and <.

Split out of D93512.

Author: Arthur O'Dwyer

libcxx/test/support/MoveOnly.h

@@ -32,7 +32,11 @@ class MoveOnly
     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 bool operator< (const MoveOnly& x) const {return data_ <  x.data_;}
+    constexpr bool operator<=(const MoveOnly& x) const {return data_ <= x.data_;}
+    constexpr bool operator> (const MoveOnly& x) const {return data_ >  x.data_;}
+    constexpr bool operator>=(const MoveOnly& x) const {return 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