[clang] [clang] Replace LLVM_ATTRIBUTE_UNUSED with [[maybe_unused]] (NFC) (PR #163914)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> This is causing a regression for me:
> 
> ```
> In file included from /local/home/ekeane/llvm-project/clang/lib/CIR/CodeGen/CIRGenDeclOpenACC.cpp:13:
> In file included from /local/home/ekeane/llvm-project/clang/lib/CIR/CodeGen/CIRGenFunction.h:17:
> In file included from /local/home/ekeane/llvm-project/clang/lib/CIR/CodeGen/CIRGenCall.h:17:
> /local/home/ekeane/llvm-project/clang/lib/CIR/CodeGen/CIRGenValue.h:311:3: error: an attribute list cannot appear here
>   311 |   [[maybe_unused]] unsigned destructedFlag : 1;

I ran into that problem before: https://github.com/llvm/llvm-project/pull/143994

I guess maybe I fixed it in the wrong way. Does moving `[[maybe_unused]]` before `LLVM_PREFERRED_TYPE` fix this for you?

https://github.com/llvm/llvm-project/pull/163914