This adds support for the OSError attributes : errno, strerror, filename and filename2.
CPython only sets errno if 2 arguments has been passed in. This has not been implemented here.
CPython OSError.args is capped at 2 items for backward compatibility reasons. This has not been
implemented here.
MICROPY_CPYTHON_COMPAT has to be enabled to get these attributes.
mp_common_errno_to_str() has been extended to check mp_errno_to_str() as well. This is done to ease
reuse for the strerror argument.
This saves code space in builds which use link-time optimization.
The optimization drops the untranslated strings and replaces them
with a compressed_string_t struct. It can then be decompressed to
a c string.
Builds without LTO work as well but include both untranslated
strings and compressed strings.
This work could be expanded to include QSTRs and loaded strings if
a compress method is added to C. Its tracked in #531.
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.
