[PATCH][RFC] Multiple target support

[Blue Swirl]

Hi,

This patch allows configuration for multiple targets, like:
./config/scripts/switch-arch amd64 cross-ppc cross-sparc32
cross-sparc64 cross-x86

The command creates directories (obj-amd64 obj-ppc obj-sparc32
obj-sparc64 obj-x86), Makefiles and other config stuff. To build all
configured targets, use:
make build
or
make build-verbose

The benefit is that after a change to a file that affect several
architectures, total recompile time is reduced greatly because only
the changed file need to be recompiled and linked. Also there is no
need to use rules.xml and config.xml links in the top level directory.

I've only tested the following targets: amd64 cross-ppc cross-sparc32
cross-sparc64 cross-x86.

Maybe with small further changes it would also be possible to put the
object directories completely outside of the source tree.

Comments?