A 32-bit libstand is needed on 64-bit platforms for use by various
bootloaders. Previously only the 32-bit version was built, installed as
/usr/lib/libstand.a.
A new 64-bit libstand consumer will arrive in the near future, so move
the bootloader-specific 32-bit version to sys/boot/libstand32/.
Explicitly link against this version in the 32-bit loaders.
Sponsored by: The FreeBSD Foundation