Unless compiled with --enable-devel=coredump, proftpd's mod_rlimit will
use a prctl(PR_SET_DUMPABLE, 0) syscall[1] which prevents us from
inspecting files open by this process[2]

We don't want to enable debug build and I did not find a way to disable
only this PR_SET_DUMPABLE flag setting.

[1] https://github.com/proftpd/proftpd/blob/v1.3.6/modules/mod_rlimit.c#L580-L583
[2] http://man7.org/linux/man-pages/man5/proc.5.html