std.Target: add tags and info for alpha, hppa, microblaze, sh + some bonus commits

[alexrp]

With this, we have target info for all architectures currently supported by Linux (except nios2, but that's at death's door anyway).

[alexrp]

@mlugg FYI ef5f413, e6ac67d :^)

You may also be delighted to know that PA-RISC has its own homegrown unwind info format like Arm.

[alexrp]

@mlugg thoughts on this? GCC makes the definition of the type dependent on the enclosing function's calling convention, which seems clearly sensible to me. The idea that there is a single global VaList type is just kinda fundamentally flawed in a world where we support multiple calling conventions for one target.

I figure we could remove std.builtin.VaList and instead make Sema pick one of the more specific decls based on calling convention. It seems like moving that logic into the compiler will also let us get rid of a lot of special-casing we do around the resolution of VaList.

[mlugg]

Sounds like you're basically hitting #24692. I think what we wanted to do here was, yeah, have @cVaStart return a callconv-dependent type. Then, @cVaArg, @cVaCopy, and @cVaEnd could probably even become userland methods on the types; I would need to check some VA ABIs to check if that works, but I would assume that inline asm can represent all of those operations once you have the actual valist value? So in the best-case scenario, @cVaStart would be the only builtin we'd need.

[alexrp]

Already passed CI and I just added a03b924 + 23b2990.