[LLVM] Make changes needed for opaque pointers (#101396)
Update llvm_codegen module to use opaque pointers feature of llvm.
* Set setOpaquePointers to true for llvm context.
* Pass Type to emit\*Load and emit\*Store functions.
* Create TypedPointer struct to keep track of Value and its Type.
* Introduce OpqTy_ to be used for opaque pointer types.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101396
Approved by: https://github.com/jgong5
