Issue #12250: regrtest --timeout displays a warning instead of failing with an

error if faulthandler.dump_tracebacks_later() is missing (e.g. if Python is
compiled without threads).

Lib/test/regrtest.py

@@ -415,12 +415,13 @@ def main(tests=None, testdir=None, verbose=0, quiet=False,
             # join it with the saved CWD so it ends up where the user expects.
             testdir = os.path.join(support.SAVEDCWD, a)
         elif o == '--timeout':
-            if not hasattr(faulthandler, 'dump_tracebacks_later'):
-                print("The timeout option requires "
-                      "faulthandler.dump_tracebacks_later", file=sys.stderr)
-                sys.exit(1)
-            timeout = float(a)
-            if timeout <= 0:
+            if hasattr(faulthandler, 'dump_tracebacks_later'):
+                timeout = float(a)
+                if timeout <= 0:
+                    timeout = None
+            else:
+                print("Warning: The timeout option requires "
+                      "faulthandler.dump_tracebacks_later")
                 timeout = None
         elif o == '--wait':
             input("Press any key to continue...")