[Replicant] [libsamsung-ipc] Add various build tests

[Denis 'GNUtoo' Carikli]

Hi,

I need to make sure that libsamsung-ipc compilation doesn't
break when merging patches.

However there are already many configurations to test:
- Replicant 4.2 (for the devices with an XMM616 modem)
- Replicant 6.0
- Replicant >=9 which will be the next Replicant version
- GNU/Linux

In all of these, the build system, compiler, and CFLAGS
do change.

Since Guix can (also) be used to build git checkouts of
projects in several different configurations (for instance
you can do several build tests each with different dependencies,
compilers, etc), it is a good fit for that.

It also takes care of all the necessary dependencies and it
is able to test the Android build system (in a limited form)
as well.

So with this patchset we should now have the proper
infrastructure to do such testing.

Fix were also done along the way to enable (again?) -Werror.

Over time I'll try to find the time to add more and more
restrictive CFLAGS to make sure that we can detect Android
breakages with such build tests.

In addition to the patches that will follow in a response to
this mail, here's an URL to the see the patches in a web interface:
https://git.replicant.us/contrib/GNUtoo/hardware_replicant_libsamsung-ipc/commit/?id=e6c2218e89f9ee403f5543675d11776a7c66fffb

And here's how to get them in a git repository:
git clone https://git.replicant.us/GNUtoo/hardware_replicant_libsamsung-ipc
cd hardware_replicant_libsamsung-ipc
git show e6c2218e89f9ee403f5543675d11776a7c66fffb

Denis.