doc: Add a "Boostrapping" section.

* doc/guix.texi (Package Modules): New node, with material formerly
  under "GNU Distribution".
  (Bootstrapping): New node.
* Makefile.am (EXTRA_DIST): Add doc/images/bootstrap-graph.dot and
  doc/images/bootstrap-graph.eps.
  (infoimagedir, dist_infoimage_DATA, DOT_OPTIONS): New variable.
  (.dot.png, .dot.eps, doc/guix.pdf, doc/guix.info, doc/guix.ps): New
  targets.
* doc/images/bootstrap-graph.dot: New file.

gnu: gcc: Add Texinfo to the native inputs.

* gnu/packages/gcc.scm (gcc-4.7): Add `native-inputs' field.
  (gcc-4.8): Remove outdated comment.
* gnu/packages/base.scm (gcc-boot0): Add `native-inputs' field.

gnu: make-bootstrap: guile-static-stripped has no "debug" output.

* gnu/packages/make-bootstrap.scm (%guile-static-stripped): Add
  `outputs' field.

build-system/gnu: Remove the "debug" output when `strip-binaries?' is #f.

* guix/build-system/gnu.scm (gnu-build, gnu-cross-build): Delete "debug"
  from OUTPUTS when STRIP-BINARIES? is false.
* gnu/packages/cross-base.scm (cross-libc): Leave `outputs' unchanged.
  This reverts commit a4627d4.

gnu: cross-libc: Remove the "debug" output.

* gnu/packages/cross-base.scm (cross-libc): Remove "debug" from the
  `outputs' field.

gnu: Add a "debug" output for some packages.

* gnu/packages/base.scm (coreutils, gnu-make, glibc): Add a "debug" output.
* gnu/packages/bdw-gc.scm (libgc): Likewise.
* gnu/packages/guile.scm (guile-2.0): Likewise.
* gnu/packages/libffi.scm (libffi): Likewise.
* gnu/packages/multiprecision.scm (gmp, mpfr, mpc): Likewise.

build-system/gnu: Write debug files to the "debug" sub-derivation, if any.

* guix/build/gnu-build-system.scm (strip): Add `objcopy-command' keyword
  parameter.
  [debug-output, debug-file-extension]: New variables.
  [debug-file, make-debug-file, add-debug-link]: New procedures.
  [strip-dir]: Use them.

utils: Re-export `alist-cons' and `alist-delete'.

* guix/build/utils.scm: Re-export `alist-cons' and `alist-delete'.

gnu: gcc: Use `gcc-configure-flags-for-triplet' when cross-compiling GCC.

* gnu/packages/cross-base.scm (gcc-configure-flags-for-triplet): Move to...
* gnu/packages/gcc.scm (gcc-configure-flags-for-triplet): ... here.  New
  procedure.
  (gcc-4.7): Use it when (%current-target-system) is true.

build: Add "mips64el-linux-gnuabi64" as a cross build target.

* build-aux/hydra/gnu-system.scm (%packages-to-cross-build): Add
  %bootstrap-tarballs.
  (%cross-targets): Add "mips64el-linux-gnuabi64".

gnu: cross-base: Add support for `mips64el-linux-gnu-gnuabi64' (N64 ABI).

* gnu/packages/cross-base.scm (gcc-configure-flags-for-triplet): New
  procedure.
  (cross-gcc): Use it.
  (xgcc-mips64el): Use *-gnuabi64 instead of the N32 ABI.

gnu: make-bootstrap: Fix cross compilation of binutils-static.

* gnu/packages/make-bootstrap.scm (%binutils-static): Inherit configure
  flags from BINUTILS.

gnu: make-bootstrap: Have %gcc-static actually static when cross building.

* gnu/packages/make-bootstrap.scm (%gcc-static): Pass `-static' through
  `LDFLAGS' when cross-compiling.

gnu: gcc: Allow cross-compilation of GCC itself.

* gnu/packages/gcc.scm (gcc-4.7): Define `CC_FOR_TARGET',
  `AR_FOR_TARGET', etc. when cross-compiling.

gnu: cross-base: Make `glibc-dynamic-linker' do the right thing.

* gnu/packages/bootstrap.scm (glibc-dynamic-linker): Determine SYSTEM
  based on (%current-target-system) when it's true.
* gnu/packages/cross-base.scm (cross-gcc): Directly call
  (package-arguments gcc-4.7) from the body of `arguments'.

gnu: cross-base: Build Binutils with `--with-sysroot=/'.

* gnu/packages/cross-base.scm (cross-binutils): Use `--with-sysroot=/'.

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.