Yes, it appears most likely to be the worker environment.  I did upgrade the kernel in between builds 250 (good) and 251 (bad), but reverting that still fails, even with the same commit as in build 250.

My current suspicion is that a test I did recently with a static 2.7.16 build is influencing the buildbot build process (which might explain why the error seems to involve an -fPIC mismatch in a library).  Not sure how yet though.