Fixes fill-kfs

Wasn't removing the libs or bins due to missing trailing slashes.
Elf loader 32/64 bit checks

KERN64 was a riscv-only thing.  CONFIG_64BIT is arch-indep (and set by
Kconfig).  Also, x86_64 can't handle 32 bit elves, though riscv can.
x86_64: pop non-sysenter TFs, fixes segmentation

Apparently we do need some data segmentation, at least for the SS, when popping
via iretq into userspace.  I haven't needed it for the kernel yet.  Note the
segment limit/base are ignored (they can't express 64 bits), but things like
the DPL and the W bit seemed to be checked.