Incorporate the OpenSMTPD' privsep crypto engine. The idea behind it is to never load the certificate' private keys in a networked process, instead they are loaded in a separate process (the `crypto' one) which signs payloads on the behalf of the server processes. This way, we greatly reduce the risk of leaking the certificate' private key should the server process be compromised. This currently compiles only on LibreSSL (portable fix is in the way).

it's better than the previous Makefile.depend approach since this automatically adapts to the included headers without requiring manual intervention to regen the list.

It uses the 'common' proc.c from various OpenBSD-daemons. gmid grew organically bit by bit and it was also the first place where I tried to implement privsep. It wasn't done very well, in fact the parent process (that retains root privileges) just fork()s a generation of servers, all sharing *exactly* the same address space. No good! Now, we fork() and re-exec() ourselves, so that each process has a fresh address space. Some features (require client ca for example) are temporarly disabled, will be fixed in subsequent commits. The "ge" program is also temporarly disabled as it needs tweaks to do privsep too.

reuse it in ge too.

it reached a point where this stuff is not maintenable. I'd like to move forward with gmid, but the restriction of capsicum and the linux environment at large that make landlock unusable (how can you resolve DNS portably when under landlock?) -and don't get me started on seccomp- makes it impossible for me to do any work. So, I prefer removing the crap, resuming working on gmid by cleaning stuff and consolidating the features, improving various things etc... and then eventually see how to introduce some sandboxing again on other systems. Patches to resume sandboxing are, as always, welcome!