[gcc r16-2579] libstdc++: provide debug impl of P2697 ctor [PR119742]

[Nathan Myers]

https://gcc.gnu.org/g:5a433ecf4da6fadc5154fa9458bda57d8a2d8ba2

commit r16-2579-g5a433ecf4da6fadc5154fa9458bda57d8a2d8ba2
Author: Nathan Myers <ncm@cantrip.org>
Date:   Mon Jul 7 16:54:26 2025 -0400

    libstdc++: provide debug impl of P2697 ctor [PR119742]
    
    This adds the new bitset constructor from string_view
    defined in P2697 to the debug version of the type.
    
    libstdc++-v3/Changelog:
            PR libstdc++/119742
            * include/debug/bitset: Add new ctor.

Diff:
---
 libstdc++-v3/include/debug/bitset | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/libstdc++-v3/include/debug/bitset b/libstdc++-v3/include/debug/bitset
index ad9b7b5c4b06..e4d3e6619c96 100644
--- a/libstdc++-v3/include/debug/bitset
+++ b/libstdc++-v3/include/debug/bitset
@@ -164,6 +164,17 @@ namespace __debug
 	       _CharT __zero, _CharT __one = _CharT('1'))
 	: _Base(__str, __pos, __n, __zero, __one) { }
 
+#ifdef __cpp_lib_bitset // ... from string_view
+      template<class _CharT, class _Traits>
+	constexpr explicit
+	bitset(std::basic_string_view<_CharT, _Traits> __s,
+	  std::basic_string_view<_CharT, _Traits>::size_type __position = 0,
+	  std::basic_string_view<_CharT, _Traits>::size_type __n =
+	    std::basic_string_view<_CharT, _Traits>::npos,
+	  _CharT __zero = _CharT('0'), _CharT __one = _CharT('1'))
+	: _Base(__s, __position, __n, __zero, __one) { }
+#endif
+
       _GLIBCXX23_CONSTEXPR
       bitset(const _Base& __x) : _Base(__x) { }