[Bug c/66970] Add __has_builtin() macro

[hpa at zytor dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66970

H. Peter Anvin <hpa at zytor dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hpa at zytor dot com

--- Comment #9 from H. Peter Anvin <hpa at zytor dot com> ---
Can I please second this request? This would be extremely useful in the Linux
kernel, *and* it would be extremely useful in any code that for whatever reason
cannot depend on any particular build system.