* guix/build/utils.scm (substitute): Change to accept a `pattern+procs'
parameter. Iterate over it.
(substitute*): Adjust accordingly.
* distro/base.scm (guile-1.8): Adjust accordingly.
* guix/build/utils.scm (let-matches, substitute*): New macros.
* distro/base.scm (guile-1.8): Use `substitute*' instead of
`substitute'. Remove the #:modules argument.
* guix/build/gnu-build-system.scm (set-paths): Dump the value of
environment variables in the `environment-variables' files, similar to
what Nixpkgs does.
* guix/build/gnu-build-system.scm (patch): New procedure.
(%standard-phases): Add `patch'.
* guix/build-system/gnu.scm (gnu-build): Add `patches' and `patch-flags'
parameters. Pass them on.
* guix/build/gnu-build-system.scm (set-paths, build, check, install):
New procedures.
(unpack): Make `source' a keyword arg; add `#:allow-other-keys'.
(configure): Likewise.
(%standard-phases): New variable.
(gnu-build): Make `source', `outputs', and `inputs' keyword arguments;
add `phases' keyword argument; #:allow-other-keys; add rest arguments
`args'. Invoke each of PHASES in order within `every'.
* guix/gnu-build-system.scm (gnu-build): Add `make-flags' and `phases'
keyword arguments. Update builder's `gnu-build' call to match the new
convention.
* guix/derivations.scm (build-expression->derivation): Add all of INPUTS
as inputs to the final derivation.
* guix/build/gnu-build-system.scm, guix/build/utils.scm,
guix/gnu-build-system.scm: New files.
* tests/builders.scm ("gnu-build"): New test.
* guix/derivations.scm (imported-modules): New procedure.
(build-expression->derivation): New keyword argument `modules'.
Use `imported-modules' when MODULES is non-empty, and pass it with
`-L' to GUILE.
* guix/build/http.scm, guix/http.scm, tests/builders.scm: New files.