This commit lets "tools/mpy_ld.py" store architecture flags in generated
MPY files if explicitly requested, like "mpy-cross" does.
To achieve this, a new command-line option ("--arch-flags") was added to
receive the architecture flags value, accepting the same arguments'
format as "mpy-cross", and performing the same input validation.
The rest of the MPY toolchain was also modified to let the user pass the
arch flags to standard native module makefiles. Given that there's
already a well-established "ARCH" argument, "ARCH_FLAGS" was chosen to
pass the optional flags to "mpy_ld.py".
Finally, documentation was updated to mention the new variable.
Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
b87d73f2e9