Do as you would in other languages: Declare symbols before using them.

package BB;
use utf8;
use Moose;
sub mysub;
use CC;
sub mysub { print "BB\n";}
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or

package BB;
use utf8;
use Moose;
sub mysub { print "BB\n";}
use CC;
[download]

Note that you can have the same problem in Perl without Moose if you export or if you have prototypes.