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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Sean Perry (perry-ca)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/135430.diff


1 Files Affected:

- (modified) clang/lib/Basic/SourceManager.cpp (+1) 


``````````diff
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"

``````````

</details>


https://github.com/llvm/llvm-project/pull/135430