PATCH: [perl #123503] Bug in POSIX::strerror on 5.21.7

PATCH: [perl #123503] Bug in POSIX::strerror on 5.21.7

There were 3 ideas for a patch: mine, Slaven's, and Father
Chrysostomos'.  I tried out all 3, and all three appear to work, without
breaking #123171.  But I chose FC's as I think it is the best.

I had to create a new .t because it turns out that the test didn't fail
when placed in the obvious test file, wrappers.t.  It appears that the
'use File::Temp' in that file perturbs things to not fail later on.
This is scary, so I created a minimal file.  I thought about using
fresh_perl, but wrappers.t needs functions from Test::More.