[clang] [Modules] No transitive source location change (PR #86912)

[Jan Svoboda via cfe-commits]

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@@ -696,7 +696,7 @@ class ASTReader
   /// Mapping from global submodule IDs to the module file in which the
   /// submodule resides along with the offset that should be added to the
   /// global submodule ID to produce a local ID.
-  GlobalSubmoduleMapType GlobalSubmoduleMap;
+  mutable GlobalSubmoduleMapType GlobalSubmoduleMap;
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jansvoboda11 wrote:

Is `mutable` necessary here?

https://github.com/llvm/llvm-project/pull/86912