I find putting a dummy statement after the call usually works fine. E.g. function_call(); 1;

sub function_call {
  print defined wantarray ? (wantarray?"list\n":"scalar\n") : "void\n"
}
sub calls_it_1 {
  print "calls_it_1: ";
  function_call();      # is this void or not?
}
sub calls_it_2 {
  print "calls_it_2: ";
  function_call(); 1;   # this is void
}

calls_it_1();
my $x = calls_it_1();
my @x = calls_it_1();
calls_it_2();
my $y = calls_it_2();
my @y = calls_it_2();

__END__

calls_it_1: void
calls_it_1: scalar
calls_it_1: list
calls_it_2: void
calls_it_2: void
calls_it_2: void
[download]