Re-add trailing whitespace to predefined-macros.txt

@sbc100 wanted to retain the whitespace trailing after certain
predefined macro lines. This change restores that whitespace from
upstream and re-generates the POSIX version using the following command:

```console
$ git diff --no-index expected/wasm32-wasi/posix/predefined-macros.txt sysroot/share/wasm32-wasi/predefined-macros.txt | sed 's/sysroot\/share\/wasm32-wasi/expected\/wasm32-wasi\/posix/' | git apply
```

Author: abrown