Build shared objects from aldor libraries

[pippijn]

In order to save on executable size, it would make sense to build shared libraries (.so/.dll) from aldor code. The problem here is that the runtime (libfoam) requires a definition of rtexns, which is in one of the standard libraries (libaldor/axllib), and the latter requires the definitions from libfoam. Thus, libfoam cannot be a shared library, but if libaldor is linked against a static libfoam, it contains the runtime, and then the user loses the choice of runtime (with -cruntime=...). Perhaps it would make sense to split the C and aldor parts of the runtime, then link the aldor part statically and the C part dynamically.