When we cached these values our idea of what they were would drift out
of sync with reality if someone (e.g., someone embedding perl) called
-sete?[ug]id() without updating C<PL_e?[ug]id>. Having to deal with
+C<sete?[ug]id()> without updating C<PL_e?[ug]id>. Having to deal with
this complexity wasn't worth it given how cheap the C<gete?[ug]id()>
system call is.