gnu: libcap: Update to 2.25.

* gnu/packages/linux.scm (libcap): Update to 2.25.

gnu: xkeyboard-config: Update to 2.19.

* gnu/packages/xorg.scm (xkeyboard-config): Update to 2.19.

gnu: xproto: Update to 7.0.31.

* gnu/packages/xorg.scm (xproto): Update to 7.0.31.

gnu: libgcrypt: Update to 1.7.4.

* gnu/packages/gnupg.scm (libgcrypt): Update to 1.7.4.

gnu: gnutls: Update to 3.5.7.

* gnu/packages/tls.scm (gnutls): Update to 3.5.7.

gnu: Default to GCC 5.

This reinstates and adjusts
commit e3d0fcbf7e55e8cbe8d0a1c5a24d73f341d7243b.

* gnu/packages/patches/gcc-libiberty-printf-decl.patch: New file.
* gnu/packages/gcc.scm (gcc-5)[source]: Use it.
[patches]: Add "gcc-arm-bug-71399.patch".
(gcc): Switch to GCC-5.
* gnu/packages/commencement.scm (libstdc++-boot0): New variable.
(gcc-boot0)[inputs]: Add it.
(gcc-toolchain-4.9): Switch to GCC-4.9.
(gcc-toolchain-5): Switch to GCC-FINAL.
* gnu/local.mk (dist_patch_DATA): Add 'gcc-libiberty-printf-decl.patch'.

gnu: sqlite: Update to 3.15.2.

* gnu/packages/databases.scm (sqlite): Update to 3.15.2.

gnu: guile: Update to 2.0.13.

* gnu/packages/guile.scm (guile-2.0): Update to 2.0.13.
[source](patches): New field.
[replacement]: Remove.
(guile-2.0.13): Remove.

gnu: grep: Update to 2.27.

* gnu/packages/base.scm (grep): Update to 2.27.

gnu: libunistring: Update to 0.9.7.

* gnu/packages/libunistring.scm (libunistring): Update to 0.9.7.
[home-page]: Use https.
[license]: License has changed to dual lgpl3+ gpl2.

gnu: coreutils: Update to 8.26.

* gnu/packages/base.scm (coreutils): Update to 8.26.

gnu: flex: Update to 2.6.2.

* gnu/packages/flex.scm (flex): Update to 2.6.2.
  [native-inputs]: Add help2man.
  [origin]: Update uri to github. Remove CVE-2016-6354 patch.
  (flex-2.6.1): Remove variable.
* gnu/packages/patches/flex-CVE-2016-6354.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Update.
* gnu/packages/kde-frameworks.scm (solid, kservice)[native-inputs]: Use
  flex.

gnu: gnutls: Update 3.5.6.

* gnu/packages/tls.scm (gnutls): Update to 3.5.6.

gnu: glibc-hurd: Force mach/hurd/libpthread subdirs to build first.

* gnu/packages/base.scm (glibc/hurd)[arguments]: Replace 'build' phase.

Co-authored-by: Ludovic Court<C3><A8>s <ludo@gnu.org>

gnu: libarchive: Update to 3.2.2.

* gnu/packages/backup.scm (libarchive): Update to 3.2.2.
[source]: Remove obsolete patches.
* gnu/packages/patches/libarchive-7zip-heap-overflow.patch,
gnu/packages/patches/libarchive-fix-filesystem-attacks.patch,
gnu/packages/patches/libarchive-fix-symlink-check.patch,
gnu/packages/patches/libarchive-safe_fprintf-buffer-overflow.patch:
Delete files.
* gnu/local.mk (dist_patch_DATA): Remove them.

gnu: libarchive: Fix typo in 'libarchive-safe_fprintf-buffer-overflow.patch'.

* gnu/packages/patches/libarchive-safe_fprintf-buffer-overflow.patch:
Use correct URL in patch documentation.

build-system/perl: Don't create non-deterministic 'perllocal.pod' files.

* guix/build/perl-build-system.scm (configure): Add "NO_PERLLOCAL=1"
to Makefile.PL arguments.

gnu: mpfr: Update to 3.1.5.

* gnu/packages/multiprecision.scm (mpfr): Update to 3.1.5.

gnu: sed: Use 'modify-phases' syntax.

* gnu/packages/base.scm (sed)[arguments]: Use 'modify-phases' syntax.

gnu: grep: Update to 2.26.

* gnu/packages/base.scm (grep): Update to 2.26.