Still to do here:
- we have a collection of syntactic accepts-invalids to diagnose
- support non-PODs in VLAs, including dynamic initialization /
destruction
- runtime checks (and throw std::bad_array_length) for bad bound
- support VLA capture by reference in lambdas
- properly support VLAs in range-based for (don't recompute bound)
llvm-svn: 179962