libprocstat: improve conditional for 32-bit compat

Include support for translating 32-bit auxv vectors on non-64-bit
platforms that aren't riscv (which has no 32-bit ABI support and
probably never will).

Reviewed by: markj
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D42201

(cherry picked from commit 248fe3d3483cb3ec2c78dd31dc02a467060a6577)