* guix/utils.scm (define-record-type*)[make-syntactic-constructor]: Bind
all the ((FIELD VALUE) ...) in a `letrec*'. Adjust `field-value'
accordingly.
* tests/utils.scm ("define-record-type* with letrec* behavior"): New
test.
* guix/utils.scm (gnu-triplet->nix-system): New procedure.
(%current-system): New variable.
* tests/utils.scm ("gnu-triplet->nix-system"): New test.
* tests/derivations.scm (%current-system): Remove. Update users to
use (%current-system) instead.
* guix/derivations.scm (derivation-path->output-path): New procedure.
(derivation-hash): Call `memoize'. In the fixed-output case, convert
HASH-ALGO to a string. In the other case, sort inputs in the
alphabetical order of their hex hash. For inputs with no sub-drvs,
add "out" as the sub-drv.
* guix/utils.scm (%nixpkgs-directory): New parameter.
(nixpkgs-derivation, memoize): New procedures.
* tests/derivations.scm ("build derivation with 1 source"): Remove
useless shebang.
(%coreutils): New variable.
("build derivation with coreutils"): New test.
* guix/utils.scm (bytevector-quintet-ref-right,
bytevector-quintet-fold): New procedures.
(bytevector-quintet-fold-right): Add `quintet-fold' parameter; use it
instead of `bytevector-quintet-fold'.
(bytevector->base32-string): Pass BYTEVECTOR-QUINTET-FOLD as the
first parameter.
(bytevector->nix-base32-string): Pass BYTEVECTOR-QUINTET-FOLD-RIGHT as
the first parameter.
* tests/utils.scm ("sha256 & bytevector->nix-base32-string"): New test.
