[clang] [clang][bytecode] Fix some shift edge cases (PR #119895)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-win-x-aarch64` running on `as-builder-2` while building `clang` at step 10 "test-check-clang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/193/builds/3970

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 10 (test-check-clang) failure: Test just built components: check-clang completed (failure)
******************** TEST 'Clang :: AST/ByteCode/shifts.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\buildbot\as-builder-2\x-aarch64\build\bin\clang.exe -cc1 -internal-isystem C:\buildbot\as-builder-2\x-aarch64\build\lib\clang\20\include -nostdsysteminc -fexperimental-new-constant-interpreter -std=c++20 -verify=expected,all C:\buildbot\as-builder-2\x-aarch64\llvm-project\clang\test\AST\ByteCode\shifts.cpp
# executed command: 'c:\buildbot\as-builder-2\x-aarch64\build\bin\clang.exe' -cc1 -internal-isystem 'C:\buildbot\as-builder-2\x-aarch64\build\lib\clang\20\include' -nostdsysteminc -fexperimental-new-constant-interpreter -std=c++20 -verify=expected,all 'C:\buildbot\as-builder-2\x-aarch64\llvm-project\clang\test\AST\ByteCode\shifts.cpp'
# .---command stderr------------
# | error: 'all-error' diagnostics seen but not expected: 
# |   File C:\buildbot\as-builder-2\x-aarch64\llvm-project\clang\test\AST\ByteCode\shifts.cpp Line 205: static assertion failed due to requirement '((wchar_t)-1U >> 31) == -1'
# | error: 'all-note' diagnostics seen but not expected: 
# |   File C:\buildbot\as-builder-2\x-aarch64\llvm-project\clang\test\AST\ByteCode\shifts.cpp Line 205: expression evaluates to '1 == -1'
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/119895