[PATCH modular 2/3 (v3)] jhbuild: Support skipping packages on a per-architecture basis.

[Jesse Adkins]

> +# There might be better ways to detect the architecture. Patches welcome.
The only thing I can think of would be the platform library.
http://docs.python.org/library/platform.html. platform.machine is
probably the way to do it. I'd bet it uses something like uname behind
the scenes.

But I'm okay with it.

Reviewed-by: Jesse Adkins <jesserayadkins at gmail.com>