Handle archive dependencies for .a files

Hi Andrzej!

I recently ran into the case where I wanted to combine several smaller libraries into a larger one. The `MAKECMD.a` command unfortunately did not handle `DEP_ARCH`, leading to an empty archive.

The change incorporates `DEP_ARCH` into creating a `.a` file. GCC doesn't like it if you do `ar rv libA.a libB.a`, so we have to re-extract the objects from the smaller libraries before recombining them into the larger archive. I would welcome a better way of expressing it in the code if you can suggest one.

Thanks!