[clang] [clang] Deduplicate the logic that only warns once when stack is almost full (PR #112371)

[Ilya Biryukov via cfe-commits]

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@@ -16,6 +16,8 @@
 
 #include <cstddef>
 
+#include "clang/Basic/Diagnostic.h"
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ilya-biryukov wrote:

This dependency seems unnecessary in this file, the other functions are lower-level (don't depend on SourceLocations, etc).

There are a few files that depend on it for things like `noteBottomOfStack()`.

In the interest of keeping the dependencies minimal, I'd suggest moving this to a new file that depends on `Stack.h` and source locations + diagnostics engine. 

https://github.com/llvm/llvm-project/pull/112371