[Serialization] Change input file content hash from size_t to uint64_t

https://reviews.llvm.org/D67249 added content hash (see
-fvalidate-ast-input-files-content) using llvm::hash_code (size_t).
The hash value is 32-bit on 32-bit systems, which was unintentional.

Fix llvm#96379: llvm#96136 switched the hash function to xxh3_64bit but did not
update the ContentHash type, leading to mismatch between ASTReader and
ASTWriter.

Author: MaskRay

clang/lib/Serialization/ASTReader.cpp

@@ -2629,7 +2629,7 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
            "We should only check the content of the inputs with "
            "ValidateASTInputFilesContent enabled.");
 
-    if (StoredContentHash == static_cast<uint64_t>(llvm::hash_code(-1)))
+    if (StoredContentHash == 0)
       return OriginalChange;
 
     auto MemBuffOrError = FileMgr.getBufferForFile(*File);

clang/lib/Serialization/ASTWriter.cpp

@@ -1776,7 +1776,7 @@ void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
     Entry.IsTopLevel = getAffectingIncludeLoc(SourceMgr, File).isInvalid();
     Entry.IsModuleMap = isModuleMap(File.getFileCharacteristic());
 
-    auto ContentHash = hash_code(-1);
+    uint64_t ContentHash = 0;
     if (PP->getHeaderSearchInfo()
             .getHeaderSearchOpts()
             .ValidateASTInputFilesContent) {
@@ -1787,12 +1787,8 @@ void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
         PP->Diag(SourceLocation(), diag::err_module_unable_to_hash_content)
             << Entry.File.getName();
     }
-    auto CH = llvm::APInt(64, ContentHash);
-    Entry.ContentHash[0] =
-        static_cast<uint32_t>(CH.getLoBits(32).getZExtValue());
-    Entry.ContentHash[1] =
-        static_cast<uint32_t>(CH.getHiBits(32).getZExtValue());
-
+    Entry.ContentHash[0] = uint32_t(ContentHash);
+    Entry.ContentHash[1] = uint32_t(ContentHash >> 32);
     if (Entry.IsSystemFile)
       SystemFiles.push_back(Entry);
     else