The quadmath detection is broken, see https://github.com/boostorg/charconv/issues/191.
Just disable quadmath.

--- a/boost/charconv/detail/config.hpp	2024-04-23 11:38:55.099806792 +0200
+++ b/boost/charconv/detail/config.hpp	2024-04-23 11:39:01.966514420 +0200
@@ -27,11 +27,6 @@
 #  define BOOST_CHARCONV_UINT128_MAX (2 * static_cast<boost::uint128_type>(BOOST_CHARCONV_INT128_MAX) + 1)
 #endif
 
-#if defined(BOOST_HAS_FLOAT128) && !defined(__STRICT_ANSI__) && !defined(BOOST_CHARCONV_NO_QUADMATH)
-#  define BOOST_CHARCONV_HAS_FLOAT128
-#  include <quadmath.h>
-#endif
-
 #ifndef BOOST_NO_CXX14_CONSTEXPR
 #  define BOOST_CHARCONV_CXX14_CONSTEXPR BOOST_CXX14_CONSTEXPR
 #  define BOOST_CHARCONV_CXX14_CONSTEXPR_NO_INLINE BOOST_CXX14_CONSTEXPR