Investigate LLVM support for huge objects

[arielb1]

LLVM does not support objects larger than 1<<61 bytes, because it represents sizes as u64 counts of bits.

Currently, to be safe, I'm blocking compile-time objects bigger than 2 GiB (in case LLVM uses an int count of bytes somewhere). It would be nice to find out how much can we increase this, especially on 64-bit targets.

[arielb1]

#18728 bounds object size by 2 GiB on 32-bit architectures and 128 TiB (1<<47) on 64-bit architectures.