the previous -Werror triggers too easily: on NixOS for example the FORTIFY_SOURCE #warning about a missing optimization level breaks all the checks when using -O0 (which is the default for non-release builds).

See https://codeberg.org/op/gmid/issues/2

so that we don't have to hardcode /etc in gmid.c. Helps on systems like FreeBSD where the non-base programs are expected to look for their config in /usr/local/etc.

this time targetting ABI level 3; partially based on how claudio@ handled it in rpki-client. Fun how this bit of code has come full circle (gmid inspired what I wrote for got, which inspired what was written for rpki-client, which has come back.)

on macos we have the situation where we have arc4random available but no getentropy().