* gnu/build/cross-toolchain.scm (set-cross-path/avr): New procedure.
(cross-gcc-build-phases) [string-prefix? "avr"]: Return
set-cross-path/avr procedure.

Signed-off-by: Jean-Pierre De Jesus DIAZ <me@jeandudey.tech>
Change-Id: I00bd39236ac2e31fef02164a7fffc8b56a166f0d
Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

* gnu/build/cross-toolchain.scm (patch-multilib-shebang): New procedure.
* gnu/packages/avr.scm (make-avr-gcc): Remove uneeded phases and flags
  for multilib.
* gnu/packages/cross-base (cross-gcc-arguments) <#:configure-flags>
  [target-avr?]: Remove --disable-multilib and add --enable-multilib.

Change-Id: Id68d803057ac898f0a670f10487b08bf0891ab0b
Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

This is a followup to 2073b55e6b964cb8ca15e8c74cb32dac00f05f0d.

* gnu/build/cross-toolchain.scm (%gcc-include-paths): Switch back to
'C_INCLUDE_PATH' & co.
* gnu/packages/cross-base.scm (%gcc-include-paths): Likewise.
(cross-gcc-arguments): Remove 'treat-glibc-as-system-header' phase.
(cross-gcc)[native-inputs]: Reorder so that libc comes last.
[search-paths]: Add "include/c++" for 'CROSS_CPLUS_INCLUDE_PATH'.
* guix/build-system/gnu.scm (standard-cross-packages): Have "cross-gcc"
appear both for 'host and 'target.

* gnu/packages/mingw.scm (mingw-w64): Update to 6.0.0.
* gnu/packages/patches/mingw-w64-6.0.0-gcc.patch: New file.
* gnu/packages/patches/mingw-w64-5.0rc2-gcc-4.9.3.patch: Delete it.
* gnu/local.mk (dist_patch_DATA): Add new patch.  Delete old patch.
* gnu/build/cross-toolchain.scm (set-cross-path/mingw): Add additional
  autoconf-like substitutions.

This patch parameterizes previously hard-coded instances of
i686-w64-mingw32, adding support for x86_64-w64-mingw32.

* gnu/packages/mingw.scm (make-mingw-w64): New procedure.
(mingw-w64-i686, mingw-w64-x86_64): New variables.
(%mingw-triplet): Remove.
(mingw-w64): Update to point to 'mingw-w64-i686'.
* gnu/packages/cross-base.scm (cross-gcc): Use 'libc' keyword argument
if specified, instead of treating it as a boolean.
(native-libc): Return the correct mingw-w64 depending on machine
specified in target.
* gnu/packages/bootstrap.scm (glibc-dynamic-linker): Add "x86_64-mingw".
* gnu/build/cross-toolchain.scm (set-cross-path/mingw): Replace
hardcoded 'i686-w64-mingw32' instances with 'target' keyword argument.
(cross-gcc-build-phases): Update accordingly; use 'target-mingw?'
implementation of target checking and add commentary.
* gnu/ci.scm (%cross-targets): Add "x86_64-w64-mingw32".

This makes sure it is inherited by packages using (cross-gcc ...).  This
commit is a followup to 01e8263febb9634564b4b73af49b81a36567a11b.

* gnu/build/cross-toolchain.scm (cross-gcc-build-phases): Move
'treat-glibc-as-system-header' phase ...
* gnu/packages/cross-base.scm (cross-gcc-arguments): ... here.

* gnu/packages/cross-base.scm (%gcc-cross-include-paths): Remove
CROSS_C_INCLUDE_PATH & co in favor of CROSS_CPATH.
* gnu/build/cross-toolchain.scm (%gcc-cross-include-paths): Likewise.
(cross-gcc-build-phases): Set CROSS_C_INCLUDE_PATH and
CROSS_CPLUS_INCLUDE_PATH when building the cross GCC.
* gnu/packages/commencement.scm (libstdc++): Add
"--disable-libstdcxx-dual-abi" to #:configure-flags.
(gcc-boot0)[arguments]: Add "--disable-libmpx"
to #:configure-flags.
(gcc-final): Add phase to set C_INCLUDE_PATH and CPLUS_INCLUDE_PATH before
building GCC.
(gcc-toolchain-5): Use MAKE-GCC-TOOLCHAIN.
(gcc-toolchain-7): Change to GCC-TOOLCHAIN.
* gnu/packages/gcc.scm (gcc): Change from GCC-5 to GCC-7.
(gfortran): Change to GFORTRAN-7.
(gcc-objc): Change to GCC-OBJC-7.
(gcc-objc++): Change to GCC-OBJC++-7.
* gnu/packages/rust.scm (rust-1.19.0)[native-search-paths]: Change from
C_INCLUDE_PATH & co to CPATH.

* gnu/build/cross-toolchain.scm (set-cross-path/mingw, install-strip): Use
invoke.