[clang] [clang-format] Add SpaceBeforeUnderscoreParens option for GNU gettext… (PR #159925)

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owenca wrote:

> > In general, we want the new option to meet the [requirements](https://clang.llvm.org/docs/ClangFormatStyleOptions.html#adding-additional-style-options). Can you link to the relevant section in GNU coding standards? It seems that this can be supported without a new option.
> 
> Hi @owenca thanks for providing feedback so quickly.
> 
> So in general I read from this that in GNU style mode, this could generally avoid separating "_(" and we wouldn not need an option. Could you please explain though what you mean with meet the requirements here? I haven't had any exposure to LLVM policies, just trying to fix some behaviour which was seen over a few years.

If click the link, you will see the requirements at the end of the section.

https://github.com/llvm/llvm-project/pull/159925