[rebranch][ClangImporter] Update hashExtension to use HashBuilder

llvm-project updated `hashExtension` in
655bea4226b401a11164f99c6344e38d8742b8e4 to use a `HashBuilder` rather
than `hash_code`. Update use in ClangImporter.

Author: bnbarham

lib/ClangImporter/ImporterImpl.h

@@ -1618,7 +1618,7 @@ class SwiftNameLookupExtension : public clang::ModuleFileExtension {
         buffersForDiagnostics(buffersForDiagnostics), availability(avail) {}
 
   clang::ModuleFileExtensionMetadata getExtensionMetadata() const override;
-  llvm::hash_code hashExtension(llvm::hash_code code) const override;
+  void hashExtension(ExtensionHashBuilder &HBuilder) const override;
 
   std::unique_ptr<clang::ModuleFileExtensionWriter>
   createExtensionWriter(clang::ASTWriter &writer) override;

lib/ClangImporter/SwiftLookupTable.cpp

@@ -1849,12 +1849,12 @@ SwiftNameLookupExtension::getExtensionMetadata() const {
   return metadata;
 }
 
-llvm::hash_code
-SwiftNameLookupExtension::hashExtension(llvm::hash_code code) const {
-  return llvm::hash_combine(code, StringRef("swift.lookup"),
-                            SWIFT_LOOKUP_TABLE_VERSION_MAJOR,
-                            SWIFT_LOOKUP_TABLE_VERSION_MINOR,
-                            version::getSwiftFullVersion());
+void
+SwiftNameLookupExtension::hashExtension(ExtensionHashBuilder &HBuilder) const {
+  HBuilder.add(StringRef("swift.lookup"));
+  HBuilder.add(SWIFT_LOOKUP_TABLE_VERSION_MAJOR);
+  HBuilder.add(SWIFT_LOOKUP_TABLE_VERSION_MINOR);
+  HBuilder.add(version::getSwiftFullVersion());
 }
 
 void importer::addEntryToLookupTable(SwiftLookupTable &table,