Unbreak 32-bit binaries on powerpc64

Recently a change was made which broke loading 32-bit binaries on powerpc64,
with an assertion in ld-elf32.so.1:

ld-elf32.so.1: assert failed:
/usr/local/poudriere/jails/ppc64/usr/src/libexec/rtld-elf/rtld.c:390

It turns out Elf32_AuxInfo was broken for a very long time on powerpc64, as
it uses long and pointers, which are both 64 bits on powerpc64, and only
manifested with the recent work on auxargs.