Doesn't help, unfortunately. It was also suggested I try making $Config{cc} local to that test script, but that changes nothing.
Nup - has to be 'blib'. The script already loads strict.pm, and I did try out 'less' and 'bytes' ... to no avail. (There may of course be some module other than 'blib' that has the same effect.)
I probably ought to take a look at blib and see what it's doing. Perhaps, therein, lies the clue.