[clang] [clang][modulemap] Lazily load module maps by header name (PR #181916)

[Michael Spencer via cfe-commits]

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@@ -1858,7 +2020,7 @@ HeaderSearch::parseAndLoadModuleMapFileImpl(FileEntryRef File, bool IsSystem,
 
   // Try to load a corresponding private module map.
   if (OptionalFileEntryRef PMMFile =
-          getPrivateModuleMap(File, FileMgr, Diags, !ParsedModuleMaps[File])) {
+          getPrivateModuleMap(File, FileMgr, Diags, false)) {
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Bigcheese wrote:

This diagnosis now happens in `parse{AndLoad}ModuleMapFile` to populate `MMState.PrivateModuleMapFile`, without this change we end up diagnosing it twice. This code changed around a lot, so it may be better to look for a way to make sure it just gets called once.

https://github.com/llvm/llvm-project/pull/181916