bug#51058: Some new details

[Hamzeh Nasajpour]

After `guix gc`, I have `xdg-utils` at this path only: 
`/gnu/store/0zdclmgw5gnpifwb7jyrmplrk13wp0yz-xdg-utils-1.1.3/`.
This `xdg-utils` has two dependencies to `xset` and `xprops` at these paths:

```
$ guix gc --references 
/gnu/store/0zdclmgw5gnpifwb7jyrmplrk13wp0yz-xdg-utils-1.1.3/
...
/gnu/store/zn8frmg17rr7jgyyzj169wrhrmsw1m63-xset-1.2.4
/gnu/store/x236bfhg4zy6bbl6hxhy9wx3pl3kz7vz-xprop-1.2.5
```

These two packages has a dependency to `libx11`:
```
$ guix gc --references /gnu/store/x236bfhg4zy6bbl6hxhy9wx3pl3kz7vz-xprop-1.2.5
...
/gnu/store/zm5x7j8vaaqr5nfrzi2ql96p5rgbj8sr-libx11-1.7.1A
```

```
$ guix gc --references /gnu/store/zn8frmg17rr7jgyyzj169wrhrmsw1m63-xset-1.2.4
...
/gnu/store/zm5x7j8vaaqr5nfrzi2ql96p5rgbj8sr-libx11-1.7.1A
```

As you see these two packages have been installed with `libx11@1.7.1A`. 

While if I install the `xdg-utils` manually:
it will be installed at 
`/gnu/store/bi4m86lripz4fhhi4c34ylg5ckxsrqzs-xdg-utils-1.1.3/`. And these are 
the references:

```
$ guix gc --references 
/gnu/store/bi4m86lripz4fhhi4c34ylg5ckxsrqzs-xdg-utils-1.1.3/
...
/gnu/store/0yfzf5wna1p5lds02pmazxm7gir8xl2k-xprop-1.2.5
/gnu/store/jg30cnk360pfrnwcfk9z2jkv0gcasa6j-xset-1.2.4
```

```
$ guix gc --references /gnu/store/0yfzf5wna1p5lds02pmazxm7gir8xl2k-xprop-1.2.5
...
/gnu/store/zyx5mhkpfyssvwljhpv5qv1iz1g2aqq3-libx11-1.6.10
```

```
$ guix gc --references /gnu/store/jg30cnk360pfrnwcfk9z2jkv0gcasa6j-xset-1.2.4
...
/gnu/store/zyx5mhkpfyssvwljhpv5qv1iz1g2aqq3-libx11-1.6.10
```

Generally the difference comes from building `libx11@1.6.10` and 
`libx11@1.7.1A`. The `libx11@1.7.1A` has been installed as default as a 
dependency of `xdg-utils`, and `libx11@1.6.10` will be installed as a 
dependency after installing the `xdg-utils` manually.

Any idea? 


--

Hamzeh Nasajpour
PantherX Team