[clang] [clang][modules] Allow module maps with textual headers to be non-affecting (PR #89441)

[Sam McCall via cfe-commits]

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@@ -237,6 +238,8 @@ GetAffectingModuleMaps(const Preprocessor &PP, Module *RootModule) {
     CollectIncludingMapsFromAncestors(CurrentModule);
     for (const Module *ImportedModule : CurrentModule->Imports)
       CollectIncludingMapsFromAncestors(ImportedModule);
+    for (const Module *UsedModule : CurrentModule->DirectUses)
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sam-mccall wrote:

I don't really understand what this change does, and all the tests pass without it. Is it related to the rest of this patch?

(Looking at the other collections that happen here, it does seem to "fit". But I don't have a really clear idea about this piece).

https://github.com/llvm/llvm-project/pull/89441