Use fewer threads when running openroad.

Don't overwhelm remote executors (which may be running multiple actions) with too many threads. Just use one unless the job is required to be run locally, in which case we expect an action will often have the entire system to itself.

place_and_route/open_road.bzl

@@ -245,14 +245,22 @@ def openroad_command(ctx, commands, input_db = None, step_name = None, inputs =
         ),
     )
 
+    # Don't overwhelm remote executors (which may be running multiple actions)
+    # with too many threads. Just use one unless the job is required to be run
+    # locally, in which case we expect an action will often have the entire
+    # system to itself.
+    num_threads = "1"
+    if "no-remote-exec" in execution_requirements:
+        num_threads = "max"
+
     ctx.actions.run(
         outputs = [output_db, log_file] + outputs,
         inputs = inputs + [command_file] + input_db_dependency,
         arguments = [
             "-no_init",
             "-no_splash",
             "-threads",
-            "max",
+            num_threads,
             "-exit",
             "-log",
             log_file.path,