Recent failures on buildfarm member hornet

hornet has failed its last five runs with

2020-10-05 22:45:42.784 UTC [34734498:40] pg_regress/create_aggregate LOG: statement: create aggregate my_percentile_disc(float8 ORDER BY anyelement) (
stype = internal,
sfunc = ordered_set_transition,
finalfunc = percentile_disc_final,
finalfunc_extra = true,
finalfunc_modify = read_write
);
TRAP: FailedAssertion("variadicArgType != InvalidOid", File: "pg_aggregate.c", Line: 216, PID: 34734498)

After looking at the commits immediately preceding the first failure, and
digging around in the aggregate-related code, it seems like commit
cc99baa43 (Improve pg_list.h's linitial(), lsecond() and co macros)
must've broke it somehow. The nearest thing that I can see to a theory
is that where DefineAggregate does
numDirectArgs = intVal(lsecond(args));
it's coming out with the wrong result, leading to a failure of the
numDirectArgs-vs-numArgs sanity check in AggregateCreate. But how could
that be? I hesitate to blame the compiler twice in one week. OTOH, it's
a not-very-mainstream compiler on a not-very-mainstream architecture.

Noah, can you poke into this in a little more detail and try to verify
what is happening?

regards, tom lane