[clang] [clang][bytecode] Don't use trunc() to increase APInt bitWidth (PR #180536)

[via cfe-commits]

github-actions[bot] wrote:

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

* 52463 tests passed
* 950 tests skipped
* 1 test failed

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

### Clang
<details>
<summary>Clang.AST/ByteCode/intap.cpp</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -cc1 -internal-isystem C:\_work\llvm-project\llvm-project\build\lib\clang\23\include -nostdsysteminc -fexperimental-new-constant-interpreter -fms-extensions -std=c++11 -verify=expected,both C:\_work\llvm-project\llvm-project\clang\test\AST\ByteCode\intap.cpp
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\23\include' -nostdsysteminc -fexperimental-new-constant-interpreter -fms-extensions -std=c++11 -verify=expected,both 'C:\_work\llvm-project\llvm-project\clang\test\AST\ByteCode\intap.cpp'
# .---command stderr------------
# | error: diagnostics with 'error' severity seen but not expected: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\AST\ByteCode\intap.cpp Line 107: width of bit-field 'foo' (1234 bits) exceeds the size of its type (128 bits)
# | error: diagnostics with 'warning' severity expected but not seen: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\AST\ByteCode\intap.cpp Line 107 'both-warning': width of bit-field 'foo' (1'234 bits) exceeds the width of its type
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--

```
</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/180536