[m-users.] Issues when upgrading from 2019-07-18 to 2019-10-16

[M McDonough]

I recently upgraded the compiler on my Windows machine, and I'm now
getting some errors when building a library:

z2_c.m:009: In module `z2_c':
z2_c.m:009:   warning: module `mglow' is imported in the interface, but it is
z2_c.m:009:   not used in the interface.
z2_c.m:011: In module `z2_c':
z2_c.m:011:   warning: module `mopus' is imported in the interface, but it is
z2_c.m:011:   not used in the interface.
z2_c.m:012: In module `z2_c':
z2_c.m:012:   warning: module `audio_loader' is imported in the interface, but
z2_c.m:012:   it is not used in the interface.
z2_c.m:013: In module `z2_c':
z2_c.m:013:   warning: module `cinnamon' is imported in the interface, but it
z2_c.m:013:   is not used in the interface.
<etc, there are many more>
`Mercury\ints\z2_c.int' and `Mercury\int2s\z2_c.int2' not written.

This module is used just to make the a library, so it contains no
actual preds, types, typeclasses, etc, only imports of the modules
that make up the library. Has something changed where this now
prevents int files from being written? I had thought that the Mercury
stdlib was built in much the same way.