Add the types for the RISC-V V extension builtins.
These types will be used by the RISC-V V intrinsics which require types of the form <vscale x 1 x i64>(LMUL=1 element size=64) or <vscale x 4 x i32>(LMUL=2 element size=32), etc. The vector_size attribute does not work for us as it doesn't create a scalable vector type. We want these types to be opaque and have no operators defined for them. We want them to be sizeless. This makes them similar to the ARM SVE builtin types. But we will have quite a bit more types. This patch adds around 60. Later patches will add another 230 or so types representing tuples of these types similar to the x2/x3/x4 types in ARM SVE. But with extra complexity that these types are combined with the LMUL concept that is unique to RISCV.
For more background see this RFC http://lists.llvm.org/pipermail/llvm-dev/2020-October/145850.html
Authored-by: Hsiangkai Wang <firstname.lastname@example.org>