plperl fails with perl 5.28

plperl fails to install with perl 5.27.11, which is to be released as 5.28.0:

2018-05-17 20:01:44.556 UTC [22629] pg_regress ERROR:
2018-05-17 20:01:44.556 UTC [22629] pg_regress CONTEXT:  while running Perl initialization
2018-05-17 20:01:44.556 UTC [22629] pg_regress STATEMENT:  CREATE EXTENSION IF NOT EXISTS "plperl"

Unfortunately this is all what I could extract from the server log,
even log_min_messages = debug5 doesn't print more.

Origin: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=899209

Christoph