[clang] [clang] Be const-correct with all uses of `Module *`. (PR #93493)

[Aaron Ballman via cfe-commits]

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@@ -817,11 +817,11 @@ class alignas(8) Decl {
            "owned local decl but no local module storage");
     return reinterpret_cast<Module *const *>(this)[-1];
   }
-  void setLocalOwningModule(Module *M) {
+  void setLocalOwningModule(const Module *M) {
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AaronBallman wrote:

This is an example where it's not clear to me that it's correct -- the caller assumes "this will never be mutated" but that's not a safe assumption given `Module *getLocalOwningModule() const;` (which itself is not const correct! that should be a pair of functions where the `const` variant returns a `const Module *` and the non-`const` variant returns a `Module *`)

https://github.com/llvm/llvm-project/pull/93493