If the user declares or defines __sancov_lowest_stack with an
unexpected type, then getOrInsertGlobal inserts a bitcast and the
following cast fails:
Constant *SanCovLowestStackConstant = M.getOrInsertGlobal(SanCovLowestStackName, IntptrTy); SanCovLowestStack = cast<GlobalVariable>(SanCovLowestStackConstant);
This variable is a SanitizerCoverage implementation detail and the user
should generally never have a need to access it, so we emit an error
now.
rdar://problem/44143130