[clang][modules] Only serialize info for locally-included headers

I noticed that some PCM files contain `HeaderFileInfo` for headers only included in a dependent PCM file, which is wasteful.

This patch changes the logic to only write headers that are included locally. This makes the PCM files smaller and saves some superfluous deserialization of `HeaderFileInfo` triggered by `Preprocessor::alreadyIncluded()`.

Author: jansvoboda11

clang/include/clang/Lex/Preprocessor.h

@@ -1490,7 +1490,7 @@ class Preprocessor {
   /// Mark the file as included.
   /// Returns true if this is the first time the file was included.
   bool markIncluded(FileEntryRef File) {
-    HeaderInfo.getFileInfo(File);
+    HeaderInfo.getFileInfo(File).IsLocallyIncluded = true;
     return IncludedFiles.insert(File).second;
   }
 

clang/lib/Lex/HeaderSearch.cpp

@@ -1582,7 +1582,6 @@ bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
     }
   }
 
-  FileInfo.IsLocallyIncluded = true;
   IsFirstIncludeOfFile = PP.markIncluded(File);
   return true;
 }

clang/lib/Serialization/ASTWriter.cpp

@@ -2163,8 +2163,8 @@ void ASTWriter::WriteHeaderSearch(const HeaderSearch &HS) {
       continue; // We have no information on this being a header file.
     if (!HFI->isCompilingModuleHeader && HFI->isModuleHeader)
       continue; // Header file info is tracked by the owning module file.
-    if (!HFI->isCompilingModuleHeader && !PP->alreadyIncluded(*File))
-      continue; // Non-modular header not included is not needed.
+    if (!HFI->isCompilingModuleHeader && !HFI->IsLocallyIncluded)
+      continue; // Header file info is tracked by the including module file.
 
     // Massage the file path into an appropriate form.
     StringRef Filename = File->getName();
@@ -2176,7 +2176,7 @@ void ASTWriter::WriteHeaderSearch(const HeaderSearch &HS) {
       SavedStrings.push_back(Filename.data());
     }
 
-    bool Included = PP->alreadyIncluded(*File);
+    bool Included = HFI->IsLocallyIncluded || PP->alreadyIncluded(*File);
 
     HeaderFileInfoTrait::key_type Key = {
       Filename, File->getSize(), getTimestampForOutput(*File)