[hurd,commited] hurd: do not check Mach and Hurd headers

[Samuel Thibault]

Joseph Myers, on sam. 03 mars 2018 22:53:23 +0000, wrote:
> I think it's dubious to have a #error requiring _GNU_SOURCE to be used, 
> because it should always be possible to write a header in a way that 
> doesn't have such a requirement.  But in any case where, after analysis, 
> such a #error is found to make sense

Notably, most Hurd interfaces use the error_t type, which is GNU-only.
I assume this is enough to make it a #error case?

Samuel