[m-rev.] for review: simplify decisions about FIMs in .int files

[Zoltan Somogyi]

For review by anyone.

This simplifies the algorithms we use to decide which foreign_import_module
items we put into .int files. This algorithm happens to generate exactly the same
.int files as the old one on the compiler, but there may be differences for other
code bases. However, even if there are, these differences are likely to consist of
the new algorithm deleting redundant foreign_import_modules that the old one
generated.

Zoltan.
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