buildall.py requires 32bit compatibility layer

[nagorny]

buildall.py requires 32bit compatibility layer but there is no information about this dependency.
The same time buildall.py has code:

    target_bits = ['64']
    if (sys.platform != 'darwin'):  # on MAC OSX we produce FAT library including both 32 and 64 bits
        target_bits.append('32')

    print("target_bits", target_bits)

suggesting that it should be somehow configured. I didn't find how to disable 32bit build. It seems to be an error.

[ekovanova]

@nagorny good catch, I've added --force_bits option to specify a bit version