[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 `clang-armv7-global-isel` running on `linaro-clang-armv7-global-isel` while building `clang` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/39/builds/3378

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

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: AST/ByteCode/shifts.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/lib/clang/20/include -nostdsysteminc -fexperimental-new-constant-interpreter -std=c++20 -verify=expected,all /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/clang/test/AST/ByteCode/shifts.cpp
+ /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/bin/clang -cc1 -internal-isystem /home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/lib/clang/20/include -nostdsysteminc -fexperimental-new-constant-interpreter -std=c++20 -verify=expected,all /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/clang/test/AST/ByteCode/shifts.cpp
error: 'all-error' diagnostics seen but not expected: 
  File /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/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 /home/tcwg-buildbot/worker/clang-armv7-global-isel/llvm/clang/test/AST/ByteCode/shifts.cpp Line 205: expression evaluates to '1 == -1'
2 errors generated.

--

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


```

</details>

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