xbps-src: generalize 32-bit masterdirs on 64-bit hosts
xbps-src: generalize 32-bit masterdirs on 64-bit hosts

Previously the check was hardcoded for i686 on x86_64. This can
however also work for ppc64 (BE) running a ppc masterdir as well
as aarch64 running armv* masterdirs.

necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages