x11-toolkits/xbae: disable tests using sbrk

[brooks]

Summary

These tests are of low value and depending on the malloc implementation
may produce false negatives. We also don't run or install them AFACT.

[brooks]

Compiled, but not tested on an amd64 world without sbrk support.

This is a bit of a sledgehammer approach so other methods might be better.

[bofh]

Looks building. Will commit on next batch.