[clang] [docs] Document the missing availability platforms and environments (PR #104653)

[Cyndy Ishida via cfe-commits]

================
@@ -1592,6 +1592,12 @@ succeeds but Clang emits a warning specifying that the function is deprecated.
 Finally, if Clang is instructed to compile code for macOS 10.7, the call
 fails because ``f()`` is no longer available.
 
+Clang is instructed to compile code for a particular OS version using the
----------------
cyndyishida wrote:

```suggestion
Clang is instructed to compile code for a minimum deployment version using the
```

https://github.com/llvm/llvm-project/pull/104653