New issue by knusbaum on void-packages repository

https://github.com/void-linux/void-packages/issues/12907
Description: ### System

* xuname:  
Void 4.19.50_1 x86_64 GenuineIntel notuptodate rmFFFFFFFFFFFFFFFF
* package:  
xbps-src, xtools

### Expected behavior
xgensum and others generate useful messages on error

### Actual behavior
```
$ xgensum -i srcpkgs/cri-tools/template 
/usr/bin/xgensum: line 32: [: too many arguments
/usr/bin/xgensum: line 36: Bootstrap: command not found
/usr/bin/xgensum: line 49: Bootstrap: command not found
```
The behavior comes as a result (i think) of these lines here:
https://github.com/void-linux/void-packages/blob/a47c2dfb5068a9cfb798df67e129b07eba97b22d/xbps-src#L260-L262

Combined with this:
https://git.vuxu.org/xtools/tree/xgensum?id=e697287c4cad3122ba4fd0efdb1a6f5966395324#n16

```
$ xdistdir 
Bootstrap packages must be updated with 'xbps-src bootstrap-update'
```

`xgensum` seems to expect xdistdir to succeed and doesn't check. What's more, the error output from xbps-src goes out on stdout rather than stderr, so the error messages get swallowed.


### Steps to reproduce the behavior
1. Have an out-of-date masterdir in void-packages.
2. try running xgensum.