[clang] [Clang][Cygwin] Use correct BuiltinVaListKind. (PR #143166)

[via cfe-commits]

https://github.com/jeremyd2019 created https://github.com/llvm/llvm-project/pull/143166

This was in older patches for Cygwin support, but was somehow lost in the latest rounds.

>From d3b165f3db087d9255c5c9e40b7636d79fc57c6e Mon Sep 17 00:00:00 2001
From: Jeremy Drake <github at jdrake.com>
Date: Fri, 6 Jun 2025 09:04:10 -0700
Subject: [PATCH] [Clang][Cygwin] Use correct BuiltinVaListKind.

This was in older patches for Cygwin support, but was somehow lost in
the latest rounds.
---
 clang/lib/Basic/Targets/X86.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index 3d58be8f898c6..b3fe98c5c742f 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -984,6 +984,10 @@ class LLVM_LIBRARY_VISIBILITY CygwinX86_64TargetInfo : public X86_64TargetInfo {
     this->WCharType = TargetInfo::UnsignedShort;
   }
 
+  BuiltinVaListKind getBuiltinVaListKind() const override {
+    return TargetInfo::CharPtrBuiltinVaList;
+  }
+
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override {
     X86_64TargetInfo::getTargetDefines(Opts, Builder);