Before that, 'guix build --substitute-urls=""' would lead to using the
daemon's own URL list instead of the empty list. The 'or*' hack, which
is to blame, had become unnecessary since commit
fb4bf72be3fbc23bca35ba4b842b7e1517ef0e3a.
Reported by Mark H Weaver <mhw@netris.org>.
* guix/scripts/substitute.scm (or*): Remove.
(%cache-urls): Use 'or' instead of 'or*'.
* tests/store.scm ("substitute query, alternating URLs"): Add test with
empty URL list.
* doc/guix.texi (Common Build Options): Mention the empty string.
71e2065a38