[libcxx-commits] [libcxx] [libc++][NFC] Remove redundant define (PR #215883)

[Louis Dionne via libcxx-commits]

ldionne wrote:

> The point of this is that it removes parsing errors later in the file when it's compiled standalone (e.g. when opened in an IDE). The `#error` doesn't actually affect how the file is parsed except for a diagnostic on that one line.

Do we do that elsewhere? We normally don't jump through hoops in the code to support IDEs AFAICT.

We should at least add a comment on that line to clarify its purpose.

https://github.com/llvm/llvm-project/pull/215883