Without this flag, mingw-w64 uses the MS implementations of snpintf and the likes.
This is not really a problem since they work with the the fixes provided for msvc,
but due to the way mingw-w64's stdio.h is structured we cannot get it to use the fixes.
io.FileIO is binary I/O, ans actually optional. Default file type is
io.TextIOWrapper, which provides str results. CPython3 explicitly describes
io.TextIOWrapper as buffered I/O, but we don't have buffering support yet
anyway.
Now schedule is: for native types, we call ->make_new() C-level method, which
should perform actions of __new__ and __init__ (note that this is not
compliant, but is efficient), but for user types, __new__ and __init__ are
called as expected.
Also, make sure we convert scalar attribute value to a bound-pair tight in
mp_obj_class_lookup() method, which avoids converting it again and again in
its callers.
stat() is bad function to use using FFI, because its ABI is largely private.
To start with, Glibc .so doesn't even have "stat" symbol. Then, layout of
struct stat is too implementation-dependent. So, introduce _os to deal
with stat() and other similar cases.