Missing getelementptr operation in the LLVM dialect

## Expected Behavior

The operation in question would be generated (alongside a pattern).

## Actual Behavior

Only the documentation is present.

## Steps to Reproduce the Problem

1. Check https://google.github.io/mlir-hs/mlir-hs-0.1.0.0/MLIR-AST-Dialect-LLVM.html#g:58

## Comments

For a couple missing operations in mlir-hs, the solution was adding missing Attributes in the Haskell side, but in this case I'm not very sure why `hs-generators.cc` refuses to generate it.