Replace STAILQ with TAILQ. TAILQs are portable enough that they can
be used on both macOS and Linux. STAILQs are not. In particular,
STAILQ_LAST does not next on Linux. Since neither STAILQ_FOREACH_SAFE
nor TAILQ_FOREACH_SAFE exist on Linux, replace its use with a regular
TAILQ_FOREACH. The _SAFE variant was only used for having the next
pointer in a local variable.