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.
