Address comments from minglotus-6

Author: Kyungwoo Lee

llvm/include/llvm/LTO/LTOBackend.h

@@ -50,7 +50,8 @@ Error backend(const Config &C, AddStreamFn AddStream,
 /// already been mapped to memory and the corresponding BitcodeModule objects
 /// are saved in the ModuleMap. If \p ModuleMap is nullptr, module files will
 /// be mapped to memory on demand and at any given time during importing, only
-/// one source module will be kept open at the most.
+/// one source module will be kept open at the most. If \p CodeGenOnly is true,
+/// the backend will skip optimization and only perform code generation.
 Error thinBackend(const Config &C, unsigned Task, AddStreamFn AddStream,
                   Module &M, const ModuleSummaryIndex &CombinedIndex,
                   const FunctionImporter::ImportMapTy &ImportList,