Windows tweak

tools/run_tests/run_tests.py

@@ -455,7 +455,6 @@ build_configs = set(cfg.build_config for cfg in run_configs)
 if args.travis:
   _FORCE_ENVIRON_FOR_WRAPPERS = {'GRPC_TRACE': 'surface,batch'}
 
-make_targets = []
 languages = set(_LANGUAGES[l]
                 for l in itertools.chain.from_iterable(
                       _LANGUAGES.iterkeys() if x == 'all' else [x]
@@ -481,10 +480,12 @@ else:
                            'CONFIG=%s' % cfg] + targets,
                           timeout_seconds=30*60)
 
-build_steps = [make_jobspec(cfg,
-                            list(set(itertools.chain.from_iterable(
-                                         l.make_targets() for l in languages))))
-               for cfg in build_configs]
+make_targets = list(set(itertools.chain.from_iterable(
+                                         l.make_targets() for l in languages)))
+build_steps = []
+if make_targets:
+  build_steps.extend(set(make_jobspec(cfg, make_targets)
+                         for cfg in build_configs))
 build_steps.extend(set(
                    jobset.JobSpec(cmdline, environ={'CONFIG': cfg})
                    for cfg in build_configs