libstdc++: Set active union member in constexpr std::string [PR103295]

Clang still complains about using std::string in constexpr contexts due
to the changes made in commit 98a0d72a. This patch ensures that we set
the active member of the union as according to [class.union.general] p6.

libstdc++-v3/ChangeLog:

	PR libstdc++/103295
	* include/bits/basic_string.h (_M_use_local_data): Set active
	member to _M_local_buf.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
(cherry picked from commit 52672be7d328df50f9a05ce3ab44ebcae50fee1b)

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 9777deaf2e91cbb33b0daf9f450c85f477e3e6c9..f1a0e6984a1f1b9e1726e1c52b6d6b0b7b6726ee 100644 (file)
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -352,8 +352,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       {
 #if __cpp_lib_is_constant_evaluated
        if (std::is_constant_evaluated())
-         for (_CharT& __c : _M_local_buf)
-           __c = _CharT();
+         for (size_type __i = 0; __i <= _S_local_capacity; ++__i)
+           _M_local_buf[__i] = _CharT();
 #endif
        return _M_local_data();
       }