Fix 64-bit build issues

Fix some type comparisons/mismatches:

- msg->what() is uint32_t (32-bit), not size_t (64-bit)
- std::max() for long long (128-bit) vs int64_t (64-bit)

Bug: 158659480
Change-Id: Ic00e6097c3ec8286e9759d286017b5e936779368