[clang] Add back include for AutoConvert.h as it's needed for z/OS (PR #135430)

[Sean Perry via cfe-commits]

https://github.com/perry-ca created https://github.com/llvm/llvm-project/pull/135430

The commit https://github.com/llvm/llvm-project/commit/a1935fd3809772c06f9a09fa151181642ae92b20 removed an include that is needed when building on z/OS.  

>From 97b19d40e42752a980c5584e758570838def193a Mon Sep 17 00:00:00 2001
From: Sean Perry <perry at ca.ibm.com>
Date: Fri, 11 Apr 2025 15:51:18 -0400
Subject: [PATCH] Add back include for AutoConvert.h as it's needed for z/OS

---
 clang/lib/Basic/SourceManager.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index a78ffc1e90ebe..6d6e54b1bec69 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -24,6 +24,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Allocator.h"
+#include "llvm/Support/AutoConvert.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Endian.h"