filesystem_utilities.c: use INODE64 on 64-bit, but not on 32-bit

[barracuda156]

Closes: #993

1. I have tested fpm on i386 with this fix, it seems to work just fine (like it does on 32-bit ppc). I tried to build several ports that use fpm, everything worked as expected. (Without this it is just broken: there is no _opendir$INODE64 for i386.)
2. While I cannot test anything on ppc64 at the moment, the symbol is in fact available in libSystem for this arch, so presumably we do not need to disable this chunk there. (__POWERPC__ is defined for ppc and ppc64 both, while __ppc__ – only for ppc.)

[perazz]

I don't have a way to test it but I'm guessing it works of course. Thanks for sharing @barracuda156, LGTM.

[barracuda156]

@perazz I guess we should be good to merge this. I won’t be able to deal with ppc64 testing soon (though I will do it eventually), but from what it looks, this should work there too. ppc is left as-is (changing the macro is inconsequential for it), i386 will be fixed by this.