[Clang] Flush minimization hints after writing (llvm#151522)

This helps to get well-formed output if Clang crashes after that point.

Author: ilya-biryukov

clang/lib/Frontend/FrontendAction.cpp

@@ -226,6 +226,8 @@ class DeserializedDeclsSourceRangePrinter : public ASTConsumer,
     }
     *OS << "  ]\n";
     *OS << "}\n";
+
+    OS->flush();
   }
 };