[clang] [Docs] Document freestanding requirements (PR #132232)

[Aaron Ballman via cfe-commits]

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@@ -534,11 +534,6 @@ <h2 id="c2x">C23 implementation status</h2>
       <td class="full" align="center">Clang 16</td>
     </tr>
     <!-- Apr 2021 Papers -->
-    <tr>
-      <td>String functions for freestanding implementations</td>
-      <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2524.htm">N2524</a></td>
-      <td class="none" align="center">No</td>
-    </tr>
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AaronBallman wrote:

N2359 applies to the compiler because it introduces new potentially reserved identifiers we may want to diagnose and it changes behavior of limits.h which Clang provides.

N2951 applies to the compiler because it imposes some requirements on freestanding regarding `FENV_ACCESS`. It's questionable whether this one belongs on the list or not. It's marked as "Unknown" currently because I've not spent the time trying to figure out whether we have anything to do here or not.

But yes, cleaning these up in a later PR is a good idea. FWIW, I've been removing ones as I realize they don't impact the compiler.

https://github.com/llvm/llvm-project/pull/132232