Gets rid of redundant double check for string type.

Also remove obsolete declaration of mp_obj_str_get_hash.

By issuing a warning that exception chaining is not supported, and ignoring
"from Y" argument.

This may be a bit confusing, as ENOENT is often rendered as "No such
file or directory", but any other code would be only more confusing.

Linking against local libffi (and other libs in future) is triggered by
"make MICROPY_STANDALONE=1". Before that, dependent libs should be built
with "make deplibs".

These tests are intended to improve coverage and provide a record of
behaviour that's either not implemented or non-compliant to CPython.

Which are currently intermixed with real scripts and spread around various
dirs.

Just dependent micropython-lib modules update for upip, no new
functionality.

Was KeyError, should be ValueError.

If byteorder of MicroPython under test and host CPython differ.

Indeed, this flag efectively selects architecture target, and must
consistently apply to all compiles and links, including 3rd-party
libraries, unlike CFLAGS, which have MicroPython-specific setting.

Some libc's may implement tgammaf as a header macro using tgamma(), so
don't assume it'll be in the library.

Latest Arch Linux doesn't have libm.so as a proper shared object and so
we need to load libm.so.6.

Also, hint about possibility to adjust heap size.

Saves 320 bytes on x86.