[Issue 22598] importC: Add support for __extension__ keyword

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=22598

--- Comment #7 from Walter Bright <bugzi...@digitalmars.com> ---
Documentation on __extension__ seems hard to come by. I found this:

https://web.mit.edu/rhel-doc/3/rhel-gcc-en-3/alternate-keywords.html

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