Question: Incremental builds for multiple build configurations side-by-side

Hello, this is not a bug, but a beginner's question.

I would like to work in a workspace, editing code which has to run on multiple architectures. There are builds working with eg: bst --option arch amd64 build mypackage.bst.

Until now (without bst) we had a CMake build directory with subdirectories for each architecture: build/mipsel or build/ppc. Each of these were configured seperately with CMake -D... --CMAKE_TOOLCHAIN_FILE=... ../.. -GNinja. For the build we just had to change to the respective builddir and issue: ninja all. This was convenient, since it allows incremental builds seperately for each architecture, using the same source.

How can I emulate this using workspaces in bst?

I have tried:

• Dumbly just building with the different arch option: ``bst --option arch i368 build mypackage.bst```. This works, but completely rebuilds and reconfigures the current _builddir. So no incremental builds.
• I've created a condition in mypackage.bst (kind: cmake) and set a different builddir dependent on the arch value (arch=i386:_builddir_i386, arch=amd64:_builddir_amd64). This does not work. When I change the arch option for the build to another value (eg. from i386 to amd64), bst only wants to issue: cmake --build _builddir_amd64. This cannot work, because the previous run only configured _builddir_i386 but not _builddir_amd64. So this won't be a solution.

Are there any other possibilities I could try?

How do others work efficiently with bst if they support multiple architectures? Is this scenario even supported by bst yet?

Thanks for any answers and help, regards Marc