Call linker even when Clflags.objfiles is empty to link .o .a files

Record when linker inputs are specified on command line.

driver/compenv.ml

@@ -600,6 +600,7 @@ let get_objfiles ~with_ocamlparam =
   else
     List.rev !objfiles
 
+let has_linker_inputs = ref false
 
 
 
@@ -653,8 +654,10 @@ let process_action
       else if Filename.check_suffix name ".cmi" && !make_package then
         objfiles := name :: !objfiles
       else if Filename.check_suffix name Config.ext_obj
-           || Filename.check_suffix name Config.ext_lib then
+           || Filename.check_suffix name Config.ext_lib then begin
+        has_linker_inputs := true;
         ccobjs := name :: !ccobjs
+      end
       else if not !native_code && Filename.check_suffix name Config.ext_dll then
         dllibs := name :: !dllibs
       else

driver/compenv.mli

@@ -37,6 +37,7 @@ val last_objfiles : string list ref
 val first_objfiles : string list ref
 
 val stop_early : bool ref
+val has_linker_inputs : bool ref
 
 type filename = string
 

driver/optmaindriver.ml

@@ -106,7 +106,8 @@ let main argv ppf =
           (Compenv.get_objfiles ~with_ocamlparam:false) target);
       Warnings.check_fatal ();
     end
-    else if not !Compenv.stop_early && !objfiles <> [] then begin
+    else if not !Compenv.stop_early &&
+            (!objfiles <> [] || !Compenv.has_linker_inputs) then begin
       let target =
         if !output_c_object then
           let s = Compenv.extract_output !output_name in