Fix Issue 711 - combining mixins and overriding causes inifite loops

[RazvanN7]

No. 7 top oldest dmd bugs.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	711	normal	combining mixins and overriding causes inifite loops

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#9908"

[jacob-carlborg]

Is the point of Bar and Bar2 to show that it doesn't matter if the mixin is placed before or after test?

[RazvanN7]

Yes. Before this patch, if the mixin was before test it would have resulted in an infinite recursion at runtime. If the mixin would have been placed after test it would have resulted in an ICE at compile time.