[clang] [clang-tools-extra] [Clang] Add support for the C `defer` TS (PR #162848)

[Srayan Jana via cfe-commits]

ValorZard wrote:

Here’s the published version of the specification:
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3589.pdf

And here’s the latest draft
https://thephd.dev/_vendor/future_cxx/technical%20specification/C%20-%20defer/C%20-%20defer%20Technical%20Specification.pdf

https://github.com/llvm/llvm-project/pull/162848