[clang] [OpenMP] Add docs for fb_nullify/fb_preserve (PR #169558)

[Abhinav Gaba via cfe-commits]

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@@ -580,6 +580,8 @@ implementation.
 | need_device_addr modifier for adjust_args clause            | :part:`partial`           | :none:`unclaimed`         | Parsing/Sema: https://github.com/llvm/llvm-project/pull/143442           |
 |                                                             |                           |                           |               https://github.com/llvm/llvm-project/pull/149586           |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
+| need_device_ptr modifier for adjust_args clause             | :part:`partial`           | :none:`unclaimed`         | Parsing/Sema: https://github.com/llvm/llvm-project/pull/168905           |
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abhinavgaba wrote:

Oh, and this should be in the OpenMP 6.1 section below.

https://github.com/llvm/llvm-project/pull/169558