Add LLVM_ATTRIBUTE_NORETURN to report_bad_alloc_error

Summary:
The attribute just means that there will be no regular return, it still
leaves room for exceptions to be thrown. It is easily verified: there
are no direct returns and the last statement is either a throw or a call
to abort.

Having the annotation helps static analyzers with this code from
Support/MemAlloc.h (slightly simplified):

LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_malloc(size_t Sz) {
  void *Result = std::malloc(Sz);
  if (Result == nullptr)
    report_bad_alloc_error("Allocation failed");
  return Result;
}

Were report_bad_alloc_error to return regularly, the function would
return nullptr, contradicting the attribute.

Reviewers: rnk, sepavloff, dblaikie, aaron.ballman

Reviewed By: dblaikie, aaron.ballman

Differential Revision: https://reviews.llvm.org/D81318