* guix/packages.scm (<package>)[inputs]: Mark as thunked.
(package-derivation)[expand-input]: Remove case where the input is a
procedure.
* tests/packages.scm ("trivial with system-dependent input"): Remove
`lambda', and use (%current-system).
* gnu/packages/bootstrap.scm (package-from-tarball): Likewise for `inputs'.
(%bootstrap-glibc, %bootstrap-gcc): Likewise.
* gnu/packages/scheme.scm (mit-scheme): Likewise.
* guix/packages.scm (<package>): Mark `arguments' as thunked.
(package-derivation): Adjust accordingly. Parameterize
%CURRENT-SYSTEM to SYSTEM, so that arguments can refer to it.
* guix/build-system/gnu.scm (package-with-explicit-inputs): Expect
`package-arguments' to always return a list, and return a list.
(package-with-extra-configure-variable): Likewise.
(static-package): Likewise.
* gnu/packages/base.scm (patch, findutils, gcc-4.7, binutils-boot0,
gcc-boot0, glibc-final-with-bootstrap-bash, cross-gcc-wrapper,
static-bash-for-glibc, binutils-final, gcc-final): Change `arguments'
from a lambda to a list, and use (%current-system) as needed.
(nix-system->gnu-triplet, boot-triplet): Have the first argument
default to (%current-system).
* gnu/packages/bootstrap.scm (glibc-dynamic-linker): Have `system'
default to (%current-system).
(%bootstrap-gcc): Change `arguments' to a list.
* gnu/packages/gawk.scm (gawk): Likewise.
* gnu/packages/m4.scm (m4): Likewise.
* gnu/packages/make-bootstrap.scm (%glibc-for-bootstrap): Likewise, and
expect `package-arguments' to return a list.
(%static-inputs, %gcc-static, tarball-package): Likewise.
* gnu/packages/ncurses.scm (ncurses): Likewise.
