./autogen.sh fails with autoconf < 2.61
The AC_C_FLEXIBLE_ARRAY_MEMBER macro was introduced in 2.61, and if you use an older version (2.59 in this case) it fails:
autoheader: warning: missing template: FLEXIBLE_ARRAY_MEMBER autoheader: Use AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], , [Description]) autoreconf: /usr/bin/autoheader failed with exit status: 1
Maybe we can provide a better warning here, to make sure that people realize they need to upgrade their autoheader?
Reported by xiando on #tor.