add support for building 32-bit RPMs on 64-bit Linux

[dpennell]

I need to build an RPM that includes a 3rd party native library and my build server is 64-bit.

If I use noarch, rpmbuild complains with:

[error] error: Arch dependent binaries in noarch package

If I use i386, rpmbuild complains with:

[error] error: No compatible architectures found for build

Running the following works:

setarch i386 sbt
rpm:packageBin

I propose to add a setarch setting in Rpm that will invoke:

setarch rpmbuild ...

If noboty objects, I'll generate a pull request shortly.

Note: running setarch <arch> sbt... is inconvenient as I have a multi-project build with each subproject generating a different rpm and one of the other sub-projects includes native 64-bit libraries.

[muuki88]

Thanks @dpennell for your request + proposal. Your suggestion sounds good. If I understand correctly setarch will is an rpm specific setting, so the setting should be named rpmSetarch.

We have a small developer guide in our wiki. Looking forward :)

[muuki88]

Closed via #786