make-kpkg per-flavour --arch option support. ...

[Sven Luther <sven.luther@wanadoo.fr>]

Hi Bastian, ...

Can i ask you to implement one arch/.../defines feature that will be needed
for the upcoming 2.6.15 packags on powerpc, and also generally useful.

We need to be able to set the make-kpkg --arch option. This option is rigth
now set with $(ARCH), which i am not sure where it comes from (maybe the
arch/ subdirectories ?), while we need to override it with an kpkg-arch option
in the same way we do the kpkg-subarch thingy right now.

Friendly,

Sven Luther