libstdc++: Use constexpr instead of _GLIBCXX20_CONSTEXPR in <vector>

For the operator<=> overload we can use the 'constexpr' keyword
directly, because we know the language dialect is at least C++20.

libstdc++-v3/ChangeLog:

	* include/bits/stl_vector.h (operator<=>): Use constexpr
	instead of _GLIBCXX20_CONSTEXPR macro.

(cherry picked from commit b6463161c3cd0b1f764697290d9569c7153b8a5b)

diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index 31169711a4892b8278428c5585e721bdc0cfd59c..b7ee62025251782f1006055354e183e3ea7440fe 100644 (file)
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -2051,7 +2051,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     { return (__x.size() == __y.size()
              && std::equal(__x.begin(), __x.end(), __y.begin())); }
 
-#if __cpp_lib_three_way_comparison
+#if __cpp_lib_three_way_comparison // >= C++20
   /**
    *  @brief  Vector ordering relation.
    *  @param  __x  A `vector`.
@@ -2064,8 +2064,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  `<` and `>=` etc.
   */
   template<typename _Tp, typename _Alloc>
-    [[nodiscard]] _GLIBCXX20_CONSTEXPR
-    inline __detail::__synth3way_t<_Tp>
+    [[nodiscard]]
+    constexpr __detail::__synth3way_t<_Tp>
     operator<=>(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
     {
       return std::lexicographical_compare_three_way(__x.begin(), __x.end(),