[llvm] [LLVM][TableGen] Check validity of IIT encoding for vector types (PR #111152)

[Rahul Joshi via llvm-commits]

jurahul wrote:

With the added assert, I get the following for `Intrinsics.td`:

```
./build/bin/llvm-tblgen -I llvm/include/ llvm/include/llvm/IR/Intrinsics.td --time-phases > d
llvm/include/llvm/IR/Intrinsics.td:376:10: error: assertion failed
  assert !or(!not(vt.isVector), !not(!empty(IIT_Vecs))),
         ^
note: Invalid IIT encoding for vector type v2048i1
llvm/include/llvm/IR/Intrinsics.td:525:5: error: assertion failed in this record
def llvm_v2048i1_ty    : LLVMType<v2048i1>;  //2048 x i1
```

https://github.com/llvm/llvm-project/pull/111152