[clang] [clang] Improve the documentation for the init_priority attribute (PR #123098)

[Steven Wu via cfe-commits]

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@@ -136,12 +137,18 @@ relative ordering of values is important. For example:
 ``Obj2`` will be initialized *before* ``Obj1`` despite the usual order of
 initialization being the opposite.
 
+Note that this attribute does not control the initialization order of objects
+across final linked image boundaries like shared objects and executables.
+
 On Windows, ``init_seg(compiler)`` is represented with a priority of 200 and
 ``init_seg(library)`` is represented with a priority of 400. ``init_seg(user)``
 uses the default 65535 priority.
 
 This attribute is only supported for C++ and Objective-C++ and is ignored in
 other language modes. Currently, this attribute is not implemented on z/OS.
+This attribute also does not control the order of initialization across
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cachemeifyoucan wrote:

I will lift this to be a parallel paragraph above:
```
On Windows, ....

On MachO platforms, ....
```

https://github.com/llvm/llvm-project/pull/123098