No preference rule for p-code languages that no ELF header field distinguishes

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With the header-field matching in angr/cle#740 in place, a good deal of p-code language selection resolves on evidence — 11,069 objects in a large corpus get a demonstrably better answer, and the ambiguous population halves. What remains is genuinely ambiguous, and picking among it needs a policy nobody has written down.

Three groups account for almost all of it. RISC-V splits between `RISCV:LE:32:default` and `RISCV:LE:32:AndeStar_v5` for 1,873 objects; 68000 has four candidate variants for 7,327; avr8 has four for 3,857. None of the Ghidra ELF opinions covering these carries a `secondary` attribute, so there is no header field to distinguish them — the ambiguity is in the opinion, not in the code that reads it. The RISC-V opinion says as much in a comment: it must choose between the `default` and `AndeStar` variants.

Today the choice falls out of `pypcode.Arch.enumerate()`, which yields in directory order, so for RISC-V it is not even stable between installations: creating the language directory repeatedly with identical contents produced both orders roughly evenly, which means a `pip install` of pypcode can change how a binary decodes. The two RISC-V languages are not interchangeable — 905 of 20,000 random 32-bit words decode differently, and one raises where the other decodes.

The obvious repair makes it worse rather than better. Sorting `Arch.enumerate()` gives determinism, but `andestar_v5.ldefs` sorts before `riscv.ldefs`, so every plain RV32 ELF would deterministically get the vendor superset. Objects observed in this group declare `.riscv.attributes` of `rv32i2p1_m2p0_a2p1_c2p0` with no Andes extension, so `default` is the correct answer for them.

So the decision is a preference rule for the remaining ambiguity — preferring a `default` variant over vendor extensions would cover RISC-V, but 68000 and avr8 want their own answer. Once that exists, sorting the enumeration is safe and worth doing for reproducibility.