It's configurable by defining MICROPY_PY_UERRNO_LIST.  If this is not
defined then a default is provided.

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.

One can instead lookup __name__ in the modules dict to get the value.

Useful to check file/dir operations result, in particular used by upip.

OSError's are now printed like:

    OSError: [Errno 1] EPERM

but only if the string corresponding to the errno is found.

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.