bug#40641: Building from git breaks when /bin/sh isn't bash

[elaexuotee]

> Wilson, could you confirm whether there's still something to fix here?
> Else, let's close this ticket and move on.

The original issue arose on a Void Linux foreign distro installation. I have
long since converted to Guix System, so cannot easily test the original
environment.

However, Void just runs dash as it's default sh, so you could be able to sanity
check with something like

    $ guix shell -C dash guix make <etc>
    $ ln -s $(command -v dash) /bin/sh
    $ ./configure --localstatedir && make