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.)

unlike the name might suggest, proc_kill() doesn't use kill(2) so proc is not needed.

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 does the unveil(2)ing based on the first config, which breaks config-reloading.

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.

fatal usually appends the error string. Add 'fatalx' that doesn't. Fix callers and move the prototypes to log.h