Supported arch names for continuous builds and sdk.gnome.org

[Tristan Van Berkom]

Hi all,

As some list readers know, we are working on ensuring builds of xdg-app 
sdks and apps on arm architectures, so one of the things I've been
doing is touching up the high level sdk build scripts so that they can
be used to produce runtimes on various arches.

While the xdg-app build tooling itself remains quite extensible to
additional arches, we should have some consensus on what specific
architectures we want to support in our high level build scripts, build
regularly and make available on sdk.gnome.org.

Right now I have been testing with 4 arch names, listed below with
their respective machine names which define how the compiler is tuned:
  x86_64  (qemux86-64)
  i686    (qemux86, which actually produces i586 code)
  aarch64 (qemuarm64)
  armv7a  (custom machine config; produces armv7-a with hard vfp float)

The referred stock machine names are defined here:
https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/conf/machine?
h=jethro

There exists a stock qemuarm machine configuration in yocto, but it
generates armv5l while modern arm with hard float is more interesting
to us (someone could later try to add a more general and widely
compatible 'arm' arch).

The naming that I arbitrarily chose aims to promise you something
compatible with the named arch; i.e. it's ok to distribute i586 code in
the i686 branch, but not ok to distribute i586 code on an i386 branch.

Any thoughts on what the arch names and characteristics should be ?

Note, I am thinking of changing armv7a for armv7a-neon (which would be
more specific by capturing the fpu property) and building neon floating
point instead of vfp.

Cheers,
    -Tristan