Generate 32bit and 64bit Machdep if possible

[sim642]

For goblint/analyzer#54.

[sim642]

Somehow opam install can spuriously sometimes fail like

# File "machdep32", line 1, characters 6-7:
# Error: Syntax error

Do modelConfigure and machdepArchConfigure executions with same binary names conflict somehow?

[michael-schwarz]

This likely requires some multiarch packages to be present. What happens when these are not present? I think we should be still able to install CIL, even if the compiler is not set up for producing 32bit executables.

[sim642]

This likely requires some multiarch packages to be present. What happens when these are not present?

These are option-al, so they'll just be None when -m32 or -m64 doesn't work. We already have something similar for generating similar models for Cilly, which also don't work on arm64 because the options are different.