[CIR] Upstream support for array types

[andykaylor]

Overview

Upstream the basic support for array variable types. The initial change should just add support for declaring and initializing global variables that are arrays of existing scalar types. Follow-up patches can add support for local variables, including dynamic-size arrays, and accessing arrays using the cir.ptr_stride operation.

Suggested minimal test case

// Global
int a[10];
int b[10] = {};
int c[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

Existing incubator tests

clang/test/CIR/CodeGen/array.c (struct test case will need to be deferred)

[AmrDeveloper]

I would like to work on it