[clang] [Clang] Rename OffloadArch::UNUSED to UNUSED_ to avoid macro collisions (PR #174528)

[via cfe-commits]

github-actions[bot] wrote:

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

The build failed before running any tests. Click on a failure below to see the details.

<details>
<summary>[code=1] tools/clang/lib/Driver/CMakeFiles/obj.clangDriver.dir/Driver.cpp.obj</summary>

```
FAILED: [code=1] tools/clang/lib/Driver/CMakeFiles/obj.clangDriver.dir/Driver.cpp.obj
sccache C:\clang\clang-msvc\bin\clang-cl.exe  /nologo -TP -DCLANG_BUILD_STATIC -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GLIBCXX_ASSERTIONS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Itools\clang\lib\Driver -IC:\_work\llvm-project\llvm-project\clang\lib\Driver -IC:\_work\llvm-project\llvm-project\clang\include -Itools\clang\include -Iinclude -IC:\_work\llvm-project\llvm-project\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:__cplusplus /Oi /Brepro /bigobj /permissive- -Werror=unguarded-availability-new /W4  -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported /Gw /O2 /Ob2  -MD -UNDEBUG /EHs-c- /GR- -std:c++17 /showIncludes /Fotools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\Driver.cpp.obj /Fdtools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\ -c -- C:\_work\llvm-project\llvm-project\clang\lib\Driver\Driver.cpp
C:\_work\llvm-project\llvm-project\clang\lib\Driver\Driver.cpp(4672,29): error: no member named 'Unknonw' in 'clang::OffloadArch'; did you mean 'Unknown'?
4672 |       (Arch == OffloadArch::Unknonw || !IsNVIDIAOffloadArch(Arch))) {
|                             ^~~~~~~
|                             Unknown
C:\_work\llvm-project\llvm-project\clang\include\clang/Basic/OffloadArch.h(20,3): note: 'Unknown' declared here
20 |   Unknown,
|   ^
1 error generated.
```
</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/174528