We can provide a basic version of mp_errno_to_str even if the uerrno
module won't be provided. Rather than looking errno names up in the
uerrno module's globals dict, we'll just rely on a simple mapping in the
function itself.
It's configured by MICROPY_PY_UERRNO_ERRORCODE and enabled by default
(since that's the behaviour before this patch).
Without this dict the lookup of errno codes to strings must use the
uerrno module itself.
If an OSError is raised with an integer argument, and that integer
corresponds to an errno, then the string for the errno is used as the
argument to the exception, instead of the integer. Only works if
the uerrno module is enabled.
Dan Halbert
Matt Wozniski
Damien George
Paul Sokolovsky