https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110077
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm testing this fix:
--- a/libstdc++-v3/src/c++17/floating_from_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
@@ -1325,7 +1325,8 @@ _ZSt10from_charsPKcS0_RDF128_St12chars_format(const char*
first,
__ieee128& value,
chars_format fmt) noexcept
__attribute__((alias ("_ZSt10from_charsPKcS0_Ru9__ieee128St12chars_format")));
-#elif defined(__FLT128_MANT_DIG__)
+#elif __FLT128_MANT_DIG__ == 113 && __LDBL_MANT_DIG__ != 113
+// Overload for _Float128 is not defined inline in <charconv>, define it here.
from_chars_result
from_chars(const char* first, const char* last, _Float128& value,
chars_format fmt) noexcept
