[clang] [CIR] Recognize constant aggregate initialization of auto vars (PR #166850)

[Amr Hesham via cfe-commits]

================
@@ -284,20 +272,13 @@ void bin_comma() {
 void compound_literal_expr() { CompleteS a = (CompleteS){}; }
 
 // CIR: %[[A_ADDR:.*]] = cir.alloca !rec_CompleteS, !cir.ptr<!rec_CompleteS>, ["a", init]
-// CIR: %[[A_ELEM_0_PTR:.*]] = cir.get_member %[[A_ADDR]][0] {name = "a"} : !cir.ptr<!rec_CompleteS> -> !cir.ptr<!s32i>
-// CIR: %[[CONST_0:.*]] = cir.const #cir.int<0> : !s32i
-// CIR: cir.store{{.*}} %[[CONST_0]], %[[A_ELEM_0_PTR]] : !s32i, !cir.ptr<!s32i>
-// CIR: %[[A_ELEM_1_PTR:.*]] = cir.get_member %[[A_ADDR]][1] {name = "b"} : !cir.ptr<!rec_CompleteS> -> !cir.ptr<!s8i>
-// CIR: %[[CONST_0:.*]] = cir.const #cir.int<0> : !s8i
-// CIR: cir.store{{.*}} %[[CONST_0]], %[[A_ELEM_1_PTR]] : !s8i, !cir.ptr<!s8i>
+// CIR: %[[CONST:.*]] = cir.const #cir.zero : !rec_CompleteS
+// CIR: cir.store align(4) %[[CONST]], %[[A_ADDR]] : !rec_CompleteS, !cir.ptr<!rec_CompleteS>
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AmrDeveloper wrote:

```suggestion
// CIR: cir.store{{.*}} %[[CONST]], %[[A_ADDR]] : !rec_CompleteS, !cir.ptr<!rec_CompleteS>
```

https://github.com/llvm/llvm-project/pull/166850