Revert "Temporarily revert LLVM commit: llvm/llvm-project#87848"

This reverts commit 0124551144c7c870d3d68271cbcb54d580e52138.

Author: devajithvs

interpreter/llvm-project/clang/lib/Lex/HeaderSearch.cpp

@@ -960,9 +960,13 @@ OptionalFileEntryRef HeaderSearch::LookupFile(
       // If we have no includer, that means we're processing a #include
       // from a module build. We should treat this as a system header if we're
       // building a [system] module.
-      bool IncluderIsSystemHeader =
-          Includer ? getFileInfo(*Includer).DirInfo != SrcMgr::C_User :
-          BuildSystemModule;
+      bool IncluderIsSystemHeader = [&]() {
+        if (!Includer)
+          return BuildSystemModule;
+        const HeaderFileInfo *HFI = getExistingFileInfo(*Includer);
+        assert(HFI && "includer without file info");
+        return HFI->DirInfo != SrcMgr::C_User;
+      }();
       if (OptionalFileEntryRef FE = getFileAndSuggestModule(
               TmpDir, IncludeLoc, IncluderAndDir.second, IncluderIsSystemHeader,
               RequestingModule, SuggestedModule)) {