[2/11][POC][Clang][RISCV] Define RVV tuple types

For the cover letter of this patch-set, please checkout D146872.

Depends on D146872.

This is the 2nd patch of the patch-set. This patch originates from
D97264. This patch further allows local variable declaration and
function parameter passing by adjustment in clang lowering.

Test cases are provided to demonstrate the LLVM IR generated.

Note: This patch is currently only a proof-of-concept with only a
single RVV tuple type declared here, the rest will be added when
the concept of this patch-set is accepted.

Authored-by: eop Chen <eop.chen@sifive.com>
Co-Authored-by: Hsiangkai Wang <kai.wang@sifive.com>

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D146873