[llvm] Remove dependence on <ciso646> (PR #73273)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-arm64-windows-msvc` running on `linaro-armv8-windows-msvc-04` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/161/builds/4607

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: ClangScanDeps/strip-visibility.c' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
rm -rf C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp
# executed command: rm -rf 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp'
# RUN: at line 2
split-file C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\clang\test\ClangScanDeps\strip-visibility.c C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp
# executed command: split-file 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\clang\test\ClangScanDeps\strip-visibility.c' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp'
# RUN: at line 3
sed -e "s|DIR|C:/Users/tcwg/llvm-worker/clang-arm64-windows-msvc/stage1/tools/clang/test/ClangScanDeps/Output/strip-visibility.c.tmp|g" C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/cdb.json.template > C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/cdb.json
# executed command: sed -e 's|DIR|C:/Users/tcwg/llvm-worker/clang-arm64-windows-msvc/stage1/tools/clang/test/ClangScanDeps/Output/strip-visibility.c.tmp|g' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/cdb.json.template'
# RUN: at line 5
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\clang-scan-deps.exe -compilation-database C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/cdb.json -format experimental-full -mode preprocess-dependency-directives > C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/result.txt
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\clang-scan-deps.exe' -compilation-database 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/cdb.json' -format experimental-full -mode preprocess-dependency-directives
# .---redirected output from 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\ClangScanDeps\Output\strip-visibility.c.tmp/result.txt'
# | {
# |   "modules": [
# |     {
# |       "clang-module-deps": [],
# |       "clang-modulemap-file": "C:\\Users\\tcwg\\llvm-worker\\clang-arm64-windows-msvc\\stage1\\tools\\clang\\test\\ClangScanDeps\\Output\\strip-visibility.c.tmp\\modules\\A\\module.modulemap",
# |       "command-line": [
# |         "-cc1",
# |         "-ferror-limit",
# |         "19",
# |         "-o",
# |         "C:/Users/tcwg/llvm-worker/clang-arm64-windows-msvc/stage1/tools/clang/test/ClangScanDeps/Output/strip-visibility.c.tmp/module-cache\\6USUGSKMHHJKB6UHPXKYO361C\\A-6USUGSKMHHJKB6UHPXKYO361C.pcm",
# |         "-disable-free",
# |         "-emit-module",
# |         "-x",
# |         "c",
# |         "C:\\Users\\tcwg\\llvm-worker\\clang-arm64-windows-msvc\\stage1\\tools\\clang\\test\\ClangScanDeps\\Output\\strip-visibility.c.tmp\\modules\\A\\module.modulemap",
# |         "-target-abi",
# |         "aapcs",
# |         "-target-cpu",
# |         "generic",
# |         "-target-feature",
# |         "+v8a",
# |         "-target-feature",
# |         "+fp-armv8",
# |         "-target-feature",
# |         "+neon",
# |         "-target-
# | ...
# `---data was truncated--------
# .---command stderr------------
# | Error while scanning dependencies for C:/Users/tcwg/llvm-worker/clang-arm64-windows-msvc/stage1/tools/clang/test/ClangScanDeps/Output/strip-visibility.c.tmp/t3.c:
# | C:/Users/tcwg/llvm-worker/clang-arm64-windows-msvc/stage1/tools/clang/test/ClangScanDeps/Output/strip-visibility.c.tmp/t3.c:1:10: fatal error: could not build module 'A'
...

```

</details>

https://github.com/llvm/llvm-project/pull/73273