[m-dev.] compiler not building with --intermodule-optimization

[Julien Fischer]

Hi,

The compiler is not currently building when --intermodule-optimization is 
enabled, due to:

    clause_to_proc.m:056: In module `check_hlds.clause_to_proc':
    clause_to_proc.m:056:   warning: module `hlds.vartypes' has a
    clause_to_proc.m:056:   `:- import_module' declaration, but is not used
    clause_to_proc.m:056:   anywhere in the module.

The fix is trivial; however, why is the warning only being triggered
when --intermodule-optimization is enabled?

Julien.