All kernels compile again, after the GCC 8 upgrade.

All 3.x kernels have been changed to use GCC 6 now, because we can't
say for sure that they boot with GCC 8 even if we made them compile
with that newer GCC. If someone wants to test a kernel for a newer
device which they can test, see the instructions on
<https://postmarketos.org/vendorkernel>.

The linux-sony-castor-windy 4.x kernel did not compile out of the box
with the latest GCC, so we set it to GCC 6 as well. This can probably
be fixed easily.

linux-teclast-x80-pro: removed Werror and updated to latest 4.14 kernel
from kernel.org, otherwise this would not compile anymore (tested with
both GCC 6 and 8, probably incompatibility with the latest binutils or
something).

This commit will take too long to compile in CI, so let's [skip ci].
I've compiled all kernels multiple times and fixed them up until all of
them were working again.

Related: #103

Network Manager does not support dhcpcd with IPv6. Fixes issue #45

(this text is copied too)
If a user has an editorconfig plugin for their editor,
it will enforce tabs instead of spaces for indentation
for APKBUILD files. It ignores other files in the repo.

I did it manually in the previous commit and replaced the wrong for
loop in gcc6-armhf. [skip ci]

I thought only having specific symlinks was enough, and it was for one
kernel. However, to make sure it works with all kernels, let's just add
symlinks for all the binutils.

Without this symlink, lots of messages like this one appear while
compiling kernels:

/bin/sh: gcc6-armv6-alpine-linux-muslgnueabihf-objdump: not found

GCC6 cross compiler packages, based on the latest pmbootstrap
aportgen code. Related: #103

With this commit, pmbootstrap!1699 and a few changes in a linux aport,
it finally compiled successfully with gcc6 \o/

Details described in #103.

* remove everything that causes conflicts when installing gcc6 and
  gcc6-armhf side by side
* fix up the existing "if cross compiling" code path to use the
  /usr/gcc6 prefix
* link binutils binaries to the locations they are expected to be
  by gcc (this took me hours to figure out....) as well as by the
  linux build system with CROSS_COMPILE
* link all gcc binaries to /usr/bin/gcc6-*

Based on the last version from Alpine, but installed to /usr/gcc6 and
with pretty much everything disabled except for the C compiler.

We can probably throw out a lot of patches, and make the APKBUILD much
smaller. But let's focus on making it possible to compile old kernels
again first. There's still a lot to do for that, see #103.

Skipping CI, because it would probably not finish building all of them.
Major breakage incoming. Details discussed here:
<https://gitlab.com/postmarketOS/pmaports/issues/103>

I've missed the patch files in the previous commit, my bad.

This reverts commit 71ffb785.

This test case only makes sense in the pmbootstrap repository, and
we have it there already. In pmaports, we don't need to check if the
"aportgen" code is working - and to check the versions of the aports
we already have the test_upstream_compatibility case.

Got the info from:
<https://developer.puri.sm/Environments/PlasmaMobile.html>

* Added linux-postmarketos-allwinner kernel
* Added copy of alpines u-boot package with pine-a64lts support
* Changed postmarketos-mkinitfs to add the plain .dtb file to the boot partition

If hildon-desktop doesn't build, then it doesn't make sense to build
the rest right now - and it's likely that this won't build either.

Build is failing.

Weston does not build for x86, because it depends on libunwind. And
libunwind is not available in Alpine for x86. I've also tried to
simply enable x86 in libunwind, but it does not build out of the box.

In order to start building again for x86 at all, let's disable weston
and all packages that depend on it on for now.

ecm_find_qmlmodule checks if QML modules are installed, and if not it
warns during build time. This is purely for packager knowledge. Not
finding those packages here doesn't affect the runtime of the
kwin_wayland at all.

We are disabling this due to bug in the qmlplugindump which causes it to
not return and get stuck, See issue #28.

Revert this when QTBUG-70460 is solved upstream.