Variability in C software is a useful tool, but critical bugs that only exist in certain configurations are easily missed by conventional debugging techniques. Even with a small number of features, the configuration space of configurable software is too large to analyze exhaustively. Variability-aware static analysis for bug detection is being developed, but remains at too early a stage to be fully usable in real-world C programs. In this work, we present a methodology of finding variability bugs by combining variability-oblivious bug detectors, static analysis of build processes, and dynamic feature interaction inference. We further present an empirical study in which we test our methodology on two highly configurable C programs. We found our methodology to be effective, finding 88 true bugs between the two programs, of which 64 were variability bugs.