add support for linux on s390/s390x

[scddev]

https://en.wikipedia.org/wiki/Linux_on_z_Systems

In our CI we are running "normal" Linux distributions like Ubuntu and Red Hat on s390/s390x.

To publish and fetch packages, we would need support for s390 (31bit, yes, gcc will need -m31) and s390x (64bit).

>>> import platform
>>> platform.system()
'Linux'
>>> platform.machine()
's390x'
>>> platform.processor()
's390x'
>>>

[lasote]

Hi, we are going to need some help here. We have to know exactly which changes would Conan need to support this:

• Support new architectures in the settings.yml file.
• The flag for the architecture in the compiler_flags.py module
• CMake requires something? Other build helpers?

If you could try manually to add the changes and verify if it works for you would be nice, honestly, it is the first time I hear about these systems.

[scddev]

Hi, no problem, I can implement it myself and prepare a PR with all the changes as soon as I have some time.