* Use `MIN` instead of similar hand rolled macro.
* Sort headers.
* Use errno.h instead of sys/errno.h.
* Wrap sizeof in parentheses.
* Remove __BSD_VISIBLE and _XOPEN_SOURCE #defines to mute warnings about
incompatible snprintf definitions.
This fixes a number of warnings I've been seeing lately in my builds.
Sort makefile variables per style.Makefile(9) (`CFLAGS`/`CWARNFLAG.gcc`) and bump `WARNS` to 3.
MFC after: 2 weeks