[Bug target/125736] GCC doesn't use implicit zero-extended register in address

[lh_mouse at 126 dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125736

--- Comment #3 from LIU Hao <lh_mouse at 126 dot com> ---
(In reply to Drea Pinski from comment #2)
> Note __seg_gs is supported for GCC except for C++.

yes the code was copied from a header that should be usable in C++, and that's
why it has `#ifdef __clang__`.