'$! = EACCESS; require ...' could fail

When require is checking against a particular entry in @INC, it stats the
potential pathname, and does various checks like skipping if it's a
directory. In this case the stat succeeds, so $! is left unchanged.
Later however, pp_require() checks for $! being EACCES. So if $! was
already set before the require, this could influence require's behaviour.