[Toybox] realpath/tar status

[enh]

(sorry for the brevity, but i'm running out of day without having had
any time to spend on this, so i'd rather say _something_ than wait
until i have more...)

feedback on realpath:
"""
./prebuilts/build-tools/path/linux-x86/realpath
/mnt/sdc/android/kernel/out --relative-to /mnt/sdc/android/kernel

For some reason it returns /out not out, which looks incorrect. Am I
using it incorrectly?
"""

-*-

as for the new tar, i updated the prebuilts yesterday and we've seen
enough OOM kills since that i've had to revert it. every case i saw
was from https://cs.android.com/android/platform/superproject/+/master:system/update_engine/Android.bp;l=947?q=ue_unittest_disk_imgs

so basically:
```
tar -jxf sample_images/sample_images.tar.bz2 -C gen disk_ext2_1k.img
disk_ext2_4k.img disk_ext2_4k_empty.img disk_ext2_unittest.img
```

(direct link to the .tar.bz2:
https://android.googlesource.com/platform/system/update_engine/+/refs/heads/master/sample_images/)

the input is pretty small:
```
~/aosp-master-with-phones/system/update_engine$ ls -lh
sample_images/sample_images.tar.bz2
-rw-r----- 1 enh primarygroup 5.9K Nov 14 18:51
sample_images/sample_images.tar.bz2
```
and the outputs are only 4MiB too, so i'm not sure what's going on
there... (and we haven't updated bzip2 since 1.0.8 in 2021, so --
although, yes, all the build tool prebuilts are updated as one -- that
didn't change, only toybox did.)