[nomaster] unbreaks test.bc

The optimizer behaves unexpectedly smartly, stripping off unused private
methods. Unfortunately, sometimes private methods might be compiled down
to public Java methods, so stripping them off might lead to binary
incompatibilities.

This particular commit recovers from this problem caused by
https://github.com/scala/scala/commit/5e715396af.
Merge pull request #2550 from scalamacros/2.10.x

[nomaster] unbreaks test.bc