Replace STAILQ with TAILQ. TAILQs are portable enough that they can

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.