build: Clearly mark Nixpkgs as optional.

* configure.ac: Always show the result of checking for Nixpkgs.  Don't
  warn when Nixpkgs is not found.
* Makefile.am (AM_DISTCHECK_CONFIGURE_FLAGS): Remove `--with-nixpkgs'
  flag.
* guix/utils.scm (%nixpkgs-directory): Use either the compile-time or
  the run-time `NIXPKGS' environment variable.
* release.nix (jobs.tarball, jobs.build): Remove `--with-nixpkgs'
  configure flag.
* README: Mark Nixpkgs as optional.

* distro/packages/databases.scm, distro/packages/guile.scm,
  distro/packages/typesetting.scm: Change uses of `nixpkgs-derivation*'
  to `nixpkgs-derivation', to avoid failing at compile-time.

distro: Build Bash sequentially.

* distro/packages/base.scm (bash): Set `#:parallel-build?' and
  `#:parallel-tests?' to #f.

build: Move `distro/patches' to `distro/packages/patches'.

* distro/patches: Move directory to...
* distro/packages/patches: ... here.
* Makefile.am (dist_patch_DATA): Adjust accordingly.
* pre-inst-env.in (DISTRO_PATCH_DIRECTORY): Likewise.

distro: Add i686-linux port.

* distro/packages/bootstrap/i686-linux/bash,
  distro/packages/bootstrap/i686-linux/mkdir,
  distro/packages/bootstrap/i686-linux/tar,
  distro/packages/bootstrap/i686-linux/xz: New files.

* distro/packages/base.scm (%bootstrap-coreutils&co,
  %bootstrap-binutils, %bootstrap-glibc, %bootstrap-gcc): Add hashes of
  the i686-linux tarballs.

* Makefile.am (bootstrap_i686_linuxdir, dist_bootstrap_i686_linux_DATA,
  nodist_bootstrap_i686_linux_DATA): New variables
  (DISTCLEANFILES): Add $(nodist_bootstrap_i686_linux_DATA).
  (distro/packages/bootstrap/i686-linux/guile-bootstrap-2.0.6.tar.xz):
  New rule.

distro: gcc: Adjust to support non-x86_64 architectures.

* distro/packages/base.scm (gcc-4.7)[arguments]: In the `pre-configure'
  phase, patch all the relevant gcc/config files, not just those for
  x86_64-linux-gnu.

utils: Remove special `substitute*' syntax for lists of files.

* guix/build/utils.scm (substitute*): Remove special syntax for
  list-of-files; instead, check whether FILE is `list?' at run time.

* distro/packages/base.scm (gcc-4.7, %binutils-static): Adjust
  accordingly.

packages: Pass `system' around.

* guix/packages.scm (package-source-derivation): Add `system'
  parameter.  Pass it to METHOD.
  (package-derivation)[expand-input]: Pass SYSTEM to
  `package-derivation' and `package-source-derivation'.

* distro/packages/base.scm (package-with-bootstrap-guile)[boot]: Pass
  SYSTEM to FETCH.

distro: Build the final inputs against the final Bash, not the bootstrap Bash.

* distro/packages/base.scm (%boot4-inputs): New variable.
  (guile-final): Use it.
  (%final-inputs): Build with %BOOT4-INPUTS, not %BOOT3-INPUTS.

distro: ncurses: Don't patch shebangs.

* distro/packages/base.scm (ncurses): Pass #:patch-shebangs? #f.

distro: Bootstrap using our own binaries instead of those from Nixpkgs.

* distro/packages/base.scm (%bootstrap-inputs): Switch to using our own
  bootstrap binaries instead of those from Nixpkgs.

distro: Build glibc with `--enable-obsolete-rpc'.

* distro/packages/base.scm (glibc-final): Pass `--enable-obsolete-rpc'.
  (%bootstrap-glibc): Update hash accordingly.

distro: Add missing Linux-Libre headers to the bootstrap glibc.

* distro/packages/base.scm (%glibc-stripped): Copy all of Linux-Libre's
  `include/asm' directory; copy a few linux/ headers too.
  (%bootstrap-glibc): Update tarball hash.

distro: Add a bootstrap GCC that uses binaries from the tarball.

* distro/packages/base.scm (%bootstrap-gcc): New variable.

distro: Add missing commands in the bootstrap binaries.

* distro/packages/base.scm (%static-inputs): Add an `awk' -> `gawk', and
  `sh' -> `bash' symlinks.  Add `fgrep' and `egrep'.
  (%bootstrap-coreutils&co): Use new tarball that contains that
  symlink.

* distro/packages/bootstrap/x86_64-linux/bash,
  distro/packages/bootstrap/x86_64-linux/mkdir,
  distro/packages/bootstrap/x86_64-linux/tar,
  distro/packages/bootstrap/x86_64-linux/xz: Use binaries from that
  tarball (the previous binaries hadn't gone through
  `remove-store-references', which is fixed now.)

distro: Update file name of initial Binutils tarball.

* distro/packages/base.scm (%bootstrap-binutils): Update remote file
  name.

distro: Update bootstrap glibc package.

* distro/packages/base.scm (%bootstrap-glibc): Update initial regexp to
  make it less Nixish.  Update hash to new tarball.

distro: Add required Linux-Libre headers to the glibc tarball.

* distro/packages/base.scm (%glibc-stripped): Include required headers
  from Linux-Libre.

distro: gcc: No longer store the absolute path of crt files.

* distro/packages/base.scm (gcc-4.7): Define
  STANDARD_STARTFILE_PREFIX_[12] instead of storing the absolute path of
  crt files.

distro: Fix GCC tarball to include the `libexec' directory.

* distro/packages/base.scm (%gcc-stripped): Copy $gcc/libexec to $out.

distro: Fix glibc tarball to include *.so.*.

* distro/packages/base.scm (%glibc-stripped): Fix regexp to
  include *.so.* in the output.