[llvm] [llvm] Fixed ItaniumDemangle.h compiled by MSVC (PR #137409)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Dmitry Vasilyev (slydiman)

<details>
<summary>Changes</summary>

If the includes tree is big enough, `llvm::itanium_demangle::PointerType` may conflict with `llvm::PointerType` from other headers. This patch fixes the following [error](https://lab.llvm.org/buildbot/#/builders/141/builds/8206):
```
C:\lldb-aarch64-windows\llvm-project\llvm\include\llvm/Demangle/ItaniumDemangle.h(617,16): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft-unqualified-friend]
  617 |   friend class PointerType;
      |                ^
      |                ::llvm::
C:\lldb-aarch64-windows\llvm-project\llvm\include\llvm/Demangle/ItaniumDemangle.h(667,24): error: 'Protocol' is a private member of 'llvm::itanium_demangle::ObjCProtoName'
  667 |       OB += objcProto->Protocol;
      |                        ^
C:\lldb-aarch64-windows\llvm-project\llvm\include\llvm/Demangle/ItaniumDemangle.h(615,20): note: implicitly declared private here
  615 |   std::string_view Protocol;
```
Few buildbots broken by #<!-- -->131836 must be green after this patch.

---
Full diff: https://github.com/llvm/llvm-project/pull/137409.diff


1 Files Affected:

- (modified) llvm/include/llvm/Demangle/ItaniumDemangle.h (+2) 


``````````diff
diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
index b4a4c72021fd1..f37905971a833 100644
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -610,6 +610,8 @@ class EnableIfAttr : public Node {
   }
 };
 
+class PointerType;
+
 class ObjCProtoName : public Node {
   const Node *Ty;
   std::string_view Protocol;

``````````

</details>


https://github.com/llvm/llvm-project/pull/137409