* guix/build-system/gnu.scm (inputs-search-paths): New procedure.
(standard-search-paths): Use it.
(expand-inputs): New procedure.
(standard-inputs): Use it.
(standard-cross-packages, standard-cross-inputs,
standard-cross-search-paths, gnu-cross-build): New procedures.
(gnu-build-system): Set `cross-build' field to `gnu-cross-build'.
* gnu/packages/cross-base.scm: Export `cross-gcc', `cross-binutils', and
`cross-libc'.
* guix/build/gnu-cross-build.scm: New file.
* Makefile.am (MODULES): Add it.
Ludovic Courtès