[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.

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