[lto] Add "could not find mkoffload" error message to lto-wrapper

2018-05-02  Tom de Vries  <tom@codesourcery.com>

	PR lto/85451
	* lto-wrapper.c (compile_offload_image): Add "could not find mkoffload"
	error message.

From-SVN: r259821

gcc/ChangeLog

+2018-05-02  Tom de Vries  <tom@codesourcery.com>
+
+	PR lto/85451
+	* lto-wrapper.c (compile_offload_image): Add "could not find mkoffload"
+	error message.
+
 2018-05-01  Marc Glisse  <marc.glisse@inria.fr>
 
 	PR tree-optimization/85143

gcc/lto-wrapper.c

@@ -749,8 +749,11 @@ compile_offload_image (const char *target, const char *compiler_path,
 	break;
       }
 
-  if (compiler)
-    {
+  if (!compiler)
+    fatal_error (input_location,
+		 "could not find %s in %s (consider using '-B')\n", suffix + 1,
+		 compiler_path);
+
   /* Generate temporary output file name.  */
   filename = make_temp_file (".target.o");
 
@@ -784,7 +787,6 @@ compile_offload_image (const char *target, const char *compiler_path,
   argv = XOBFINISH (&argv_obstack, char **);
   fork_execute (argv[0], argv, true);
   obstack_free (&argv_obstack, NULL);
-    }
 
   free_array_of_ptrs ((void **) paths, n_paths);
   return filename;