* guix/build/utils.scm (alist-cons-before)
(alist-cons-after): Error with a match failure if the
reference is not found, instead of appending to the alist.
* tests/build-utils.scm: Update tests to match the new behavior.
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Change-Id: I3044b101bd06231d5cd55a544ac1009e6ce6f9a0