CPython docs explicitly state that the RHS of a set/frozenset binary op
must be a set to prevent user errors. It also preserves commutativity of
the ops, eg: "abc" & set() is a TypeError, and so should be set() & "abc".
This change actually decreases unix (x64) code by 160 bytes; it increases
stm32 by 4 bytes and esp8266 by 28 bytes (but previous patch already
introduced a much large saving).
For these 3 bitwise operations there are now fast functions for
positive-only arguments, and general functions for arbitrary sign
arguments (the fast functions are the existing implementation).
By default the fast functions are not used (to save space) and instead
the general functions are used for all operations.
Enable MICROPY_OPT_MPZ_BITWISE to use the fast functions for positive
arguments.
