macOS 10.13 illegal instruction

Hi there,

 

While trying to build from source on the master branch on my mac today, I encountered the same vasnprintf bug mentioned for gnulib here: https://lists.gnu.org/archive/html/bug-gnulib/2017-07/msg00056.html

 

The symptom is that the build fails during docs build because src/m4 gives an "illegal instruction" exception, caused by vasnprintf allowing %n. It can be solved by applying the same patch from the above thread to the provided gnulib. I think for m4 that it will be sufficient to update the gnulib subrepo to a more recent commit.

 

Thanks,

Jon