[CIR] Upstream VectorType support

[AmrDeveloper]

Overview

Upstream, the basic support for vector types. The initial change should add support for declaring and initialising global variables that are a vector of existing scalar types. Follow-up patches can add support for local variables accessing elements and perform vector op.

Suggested minimal test case

typedef int vi4 __attribute__((vector_size(16)));

vi4 a = { 1, 2, 3, 4 };
vi4 b = { x, 5, 6, x + 1 };

Existing incubator tests

clang/test/CIR/CodeGen/vectype.c
clang/test/CIR/CodeGen/vectype-ext.c