unidasm: Support for architecture subset options

[brycecherry75]

A number of architectures listed by this utility comprise a number of variants e.g. Motorola 68000 family and certain architectures such as the x86 family have a number of instruction subsets supported in certain members of this family - support for this feature would help find invalid instructions for an architecture supporting certain instruction subsets and help compact the number of architectures in the list displayed when run without any parameters.

[ajrhacker]

This is not really a simple feature request, but two feature requests in one: more support for instruction subsets, and a method of specifying architectural variants for unidasm. In some cases, such as Motorola 68000, the subsets are already in unidasm but listed as separate architectures.

With regard to instruction subsets, the question isn't always subsetting per se: lots of architectural variants have unique instructions (especially if one includes officially undocumented instructions) or incompatible encodings for the same instructions (already an issue with the x86's 16-bit and 32-bit modes). Anyone doing reverse engineering might also want to arbitrarily further restrict the "valid" instruction set to exclude instructions that pertain to, say, irrelevant data types or unused calling conventions.

On top of instruction set variations, many of the architectures MAME supports are microcontroller families where each model group also has its own set of special function registers.