[Bug middle-end/126625] hwint.cc reflect_hwi () should use __builtin_bitreverse64 if supported.

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126625

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Maybe it could use __has_builtin(__builtin_bitreverse64) instead to support
clang too?