distro: bash, readline: Correctly set RUNPATH to the dependencies.

* distro/base.scm (readline): Add configure flags to set an rpath on
  ncurses.
  (bash): Add configure flags to set an rpath to readline and ncurses.

distro: Add bzip2.

* distro/base.scm (bzip2): New variable.
  (%final-inputs): Add bzip2.

distro: Bootstrap standard inputs from Nixpkgs.

This is a first step towards bootstrapping from a set of pre-built,
statically-linked binaries.

* guix/build-system/gnu.scm (package-with-explicit-inputs,
  standard-inputs): New procedure.
  (%store): New variable.
  (%standard-inputs): Remove.
  (gnu-build): New `implicit-inputs?' keyword parameter.  Use it to
  choose whether to use `(standard-inputs SYSTEM)' or the empty list.

* distro/base.scm (guile-2.0): Remove dependency on XZ, which is now
  implicit.
  (%bootstrap-inputs, gcc-boot0, binutils-boot0, linux-headers-boot0,
  %boot1-inputs, glibc-final, %boot2-inputs, m4-boot2, gmp-boot2,
  mpfr-boot2, mpc-boot2, %boot3-inputs, gcc-final, %boot4-inputs,
  %final-inputs): New variables.

packages: Add `package-transitive-propagated-inputs'.

* guix/packages.scm (transitive-inputs): New procedure.
  (package-transitive-inputs): Rewrite in terms of `transitive-inputs'.
  (package-transitive-propagated-inputs): New procedure.

packages: Cache the result of `package-derivation'.

* guix/packages.scm (%derivation-cache): New variable.
  (cache, cached-derivation): New procedures.
  (package-derivation): Use them.

distro: recutils: Allow builds with glibc 2.16+.

* distro/base.scm (recutils): Apply. `diffutils-gets-undeclared.patch'.

distro: glibc: Propagate Linux headers.

* distro/base.scm (glibc): Move LINUX-HEADERS from `native-inputs' to
  `propagated-inputs'.  Remove unnecessary `_' in /bin/pwd substitution.

distro: diffutils: Allow builds with glibc 2.16+.

* distro/patches/diffutils-gets-undeclared.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.

* distro/base.scm (diffutils): Apply. `diffutils-gets-undeclared.patch'.

distro: tar: Allow builds with glibc 2.16+.

* distro/patches/tar-gets-undeclared.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.

* distro/base.scm (tar): Apply. `tar-gets-undeclared.patch'.

packages: Add a printer for <package>.

* guix/packages.scm (<package>): Add record printer.

Optimize `write-derivation' and `derivation-path->output-path'.

* guix/derivations.scm (write-derivation): Explicitly use
  `simple-format'.
  (derivation-path->output-path): Memoize.

Optimize `store-path?'.

* guix/store.scm (store-path?): Check with `string-prefix?' instead of a
  regexp.

build-system/gnu: Really apply patches.

* guix/build/gnu-build-system.scm (patch): Use `--input FILE', not just
  `FILE'.

utils: Change `substitute*' to allow iteration over several matches.

* guix/build/utils.scm (substitute): Do not pass the OUT to PROC; use
  `list-matches' instead of `regexp-exec' and pass a list of matches to
  PROC. Expect PROC to return a string, and output that.  Fold over
  RX+PROC in order.  Use `(read-line p 'concat)' to include the trailing
  delimiter in LINE.
  (substitute*): Produce code to iterate over the matches, and return a
  string, which includes anything from the original line that's in
  between matches.

* distro/base.scm (gcc-4.7, glibc): Adjust accordingly: remove use
  of (ice-9 regex) and `regexp-substitute/global'; return a string.

distro: m4: Add patch to allow builds with glibc 2.16+.

* distro/base.scm (m4): Use `m4-gets-undeclared.patch'.

* distro/patches/m4-gets-undeclared.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.

Add a `guile-for-build' parameter to `build-expression->derivation'.

* guix/derivations.scm (%guile-for-build): Use `nixpkgs-derivation*'
  instead of `nixpkgs-derivation'.
  (build-expression->derivation): New `guile-for-build' keyword
  parameter.  Use it.

Add an `env-vars' keyword parameter to `build-expression->derivation'.

* guix/derivations.scm (build-expression->derivation): New `env-vars'
  keyword parameter; default to '().  Use it.

build-system/gnu: Add `path-exclusions' parameter.

* guix/build/gnu-build-system.scm (set-paths): Add new `path-exclusions'
  parameter; honor it.
* guix/build-system/gnu.scm (gnu-build): New `path-exclusions' keyword
  parameter; pass it to BUILDER.

* distro/base.scm (gcc-4.7): Exclude "libc" from $LIBRARY_PATH.

distro: gcc: Allow `libstdc++' to be found.

* distro/base.scm (gcc-4.7): Add `-rpath' arguments to `LIB_SPEC' to
  allow `libstdc++' to be found by users.

distro: gcc: Pass #:strip-binaries?.

* distro/base.scm (gcc-4.7): Pass #:strip-binaries?.