This is another revised series for checking for bounds consistency when assigning VM types.
Based on feedback, I disentangled this from UBSan for a three reasons: - I think it makes sense as a stand-alone feature similar to other run-time instrumentation features GCC already has. - Not all checks are strictly speaking for UB, i.e. it triggers for strictly conforming code which has inconsistent bounds. For this feature, it makes sense to assume that bounds are correct (and GCC warns about inconsistently declared bounds by default already for a while). - So far, there is no upstream support in libubsan which we could use. Bootstrapped and regression tested on x86_64. Martin
