Add TCG meta-architecture support

[pgoodman]

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Bringing up new architectures is challenging, and even for supported architectures, there remain many instructions that we don't model. QEMU's Tiny Code Generator (TCG) is a permissively licensed library used by QEMU for dynamic translation of machine code instructions to an intermediate form for later JIT-compiling. It should be possible to treat TCG as an architecture or meta-architecture of its own in Remill, defining the semantics of TCG instructions using DEF_SEM and DEF_ISEL. In theory, by supporting TCG, we could support the architectures that TCG supports, which are numerous.

[adrianherrera]

This is a greatl idea! Maybe you can check out what S2E and RevGen do and see if there are any useful ideas there. Yeah, shameless plug :)

[pgoodman]

My understanding of the major complexity of this issue is that it's more than just "support TCG": it's about supporting the individual CPU implementations of QEMU which generate TCG.