[clang] [Clang] fix bad codegen from constexpr structured bindings (PR #186594)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 53249 tests passed
* 1025 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang
<details>
<summary>Clang.CodeGenCXX/cpp26-constexpr-binding-pack-subscript.cpp</summary>

```
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -std=c++26 -O3 -emit-llvm -S -target x86_64-unknown-linux-gnu -o - C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp | c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -std=c++26 -O3 -emit-llvm -S -target x86_64-unknown-linux-gnu -o - 'C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp'
# .---command stderr------------
# | C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp:9:10: fatal error: 'array' file not found
# |     9 | #include <array>
# |       |          ^~~~~~~
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe' 'C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp'
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\clang\test\CodeGenCXX\cpp26-constexpr-binding-pack-subscript.cpp
# `-----------------------------
# error: command failed with exit status: 2

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/186594