Fix two bugs for 64-bit slang.

The first is to handle structs in invoke parameter lists by assuming struct and
not struct*. The second is to not cache LLVM types for RS object types because
it breaks on 64-bit compilation.

Cherry-pick of d56a92fc2b1d417ce53d9550548fe1661fa37d40

Change-Id: I26d7dd7395ef0146eb84d43cbec5cf8d49d09697
3 files changed