build: Build the bootstrap tarballs on Hydra.

* build-aux/hydra/gnu-system.scm (%packages-to-cross-build): Uncomment
  the bootstrap tarball packages.

gnu: make-bootstrap: Allow cross-compilation of the bootstrap tarballs.

* gnu/packages/make-bootstrap.scm (package-with-relocatable-glibc): Turn
  `inputs' into a thunk.  Add `native-inputs', and pass it to
  `package-with-explicit-inputs'.
  (%static-inputs): Add %BASH-STATIC as an input to gawk when cross
  building.
  (%glibc-stripped): When cross compiling,
  use (glibc-for-bootstrap (cross-libc)) as the basis.
  (%gcc-static): Base on GCC-4.7, not GCC-FINAL.
  (tarball-package): TAR and XZ are native inputs.  Choose the tarball
  file name based on (%current-target-system) too.

build-system/gnu: `package-with-explicit-inputs' skips non-GBS packages.

* guix/build-system/gnu.scm (package-with-explicit-inputs)[rewritten-input]:
  Leave P unchanged if its build system is not GNU-BUILD-SYSTEM.

gnu: cross-base: Make the cross tools native inputs.

* gnu/packages/cross-base.scm (cross-gcc): Change `inputs' to
  `native-inputs', and set `inputs' to the empty list.
  (cross-libc): Likewise.

build-system/gnu: Augment `package-with-explicit-inputs' for cross builds.

* guix/build-system/gnu.scm (package-with-explicit-inputs): Add
  `native-inputs' keyword parameter.  Allow INPUTS and NATIVE-INPUTS to
  be thunks.

build-system/trivial: Don't bind `%target' in the builder.

* guix/build-system/trivial.scm (trivial-cross-build): Don't bind
  `%target' here since this causes problem when BUILDER
  contains (use-modules ...) clauses, and can be achieved differently
  anyway.

gnu: gawk: Allow cross-compilation.

* gnu/packages/gawk.scm (gawk)[arguments]: Annihilate the
  `check-for-shared-lib-support' target when cross-compiling.

build-system/gnu: Disable test suite when cross building.

* guix/build-system/gnu.scm (gnu-cross-build): Change #:tests? to
  default to #f.

gnu: libffi: Upgrade to 3.0.13.

* gnu/packages/libffi.scm (libffi): Upgrade to 3.0.13.

utils: `set-path-environment-variable' calls `unsetenv' for empty values.

* guix/build/utils.scm (set-path-environment-variable): When VALUE is
  the empty string, call `unsetenv' instead of `setenv'.
* gnu/packages/guile.scm (guile-2.0)[arguments]: Remove `unsetenv'
  trick.

gnu: acl, attr: Make `gettext' a native input.

* gnu/packages/acl.scm (acl): Make `gettext' a native input, always.
* gnu/packages/attr.scm (attr): Likewise.

gnu: gmp: Upgrade to 5.1.2.

* gnu/packages/multiprecision.scm (gmp): Update to 5.1.2.

gnu: gawk: Upgrade to 4.1.0.

* gnu/packages/gawk.scm (gawk): Update to 4.1.0.  Remove wrong-headed
  comments.

gnu: gzip: Upgrade to 1.6.

* gnu/packages/compression.scm (gzip): Upgrade.

build-system/gnu: Set #:tests? to #f when cross-compiling.

* guix/build/gnu-build-system.scm (check): Add `target' formal
  parameter.  Change `tests?' to default to (not target).

build-system/gnu: Save `environment-variables' after each phase.

* guix/build/gnu-build-system.scm (set-paths): Move `system' call to...
  (gnu-build): ... here.

build-system/gnu: Unify with (guix build-system gnu-cross-build).

* guix/build/gnu-build-system.scm (set-paths): Add `native-inputs' and
  `native-search-paths' keyword parameters.  Honor them.
  (configure): Add `target' and `native-inputs' keyword parameters.
  Look for Bash in NATIVE-INPUTS or INPUTS.  Pass `--host' when TARGET
  is true.
  (strip): Add `strip-command' keyword parameter.  Use it.
* guix/build/gnu-cross-build.scm: Remove.
* Makefile.am (MODULES): Adjust accordingly.
* gnu/packages/acl.scm, gnu/packages/attr.scm, gnu/packages/base.scm,
  gnu/packages/bash.scm, gnu/packages/gawk.scm,
  gnu/packages/gettext.scm, gnu/packages/guile.scm,
  gnu/packages/libffi.scm, gnu/packages/libsigsegv.scm,
  gnu/packages/linux.scm, gnu/packages/ncurses.scm,
  gnu/packages/readline.scm, guix/build-system/gnu.scm: Replace
  `%standard-cross-phases' by `%standard-phases'.  Remove references
  to (guix build gnu-cross-build).

Merge branch 'master' into core-updates

Conflicts:
	gnu/packages/make-bootstrap.scm

gnu: libgc: Always build with -DUSE_LIBC_PRIVATES.

* gnu/packages/bdw-gc.scm (libgc): Add `arguments' field.
* gnu/packages/make-bootstrap.scm (%guile-static): Remove local `libgc'.

gnu: libgc: Switch to 7.2d.

* gnu/packages/bdw-gc.scm (libgc): Upgrade to 7.2d.
  (libgc-7.2): Remove.