libprocstat: improve conditional for 32-bit compat

[brooks]

Summary

Include support for translating 32-bit auxv vectors on non-64-bit
platforms that aren't riscv (which has no 32-bit ABI support).

[markj]

I don't see a problem, but why bother hard-coding the platforms that lack 32-bit compat support?

[brooks]

In D42201#962809, @markj wrote:

I don't see a problem, but why bother hard-coding the platforms that lack 32-bit compat support?

In this case it's not a lack of 32-bit compat support so much as there will never be 32-bit support. Why compile code gated by an always false, dynamic check? I guess we might end up with an x32 interface if someone really needed the smaller pointer size, but I suspect that would have a different sv_name and this ifdef would be the least of a developer implementing x32's concerns.