[analyzer] DeadStores: Add a crude suppression files generated by DriverKit IIG.
IIG is a replacement for MIG in DriverKit: IIG is autogenerating C++ code.
Suppress dead store warnings on such code, as the tool seems to be producing
them regularly, and the users of IIG are not in position to address these
warnings, as they don't control the autogenerated code. IIG-generated code
is identified by looking at the comments at the top of the file.
Differential Revision: https://reviews.llvm.org/D63118