Fix #10003. Add SIGBREAK to the set of valid signals on Windows.

This fixes a regression noticed by bzr, introduced by issue #9324.
diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index 7aa03ef..1f15ff7 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -212,13 +212,13 @@
 @unittest.skipUnless(sys.platform == "win32", "Windows specific")
 class WindowsSignalTests(unittest.TestCase):
     def test_issue9324(self):
+        # Updated for issue #10003, adding SIGBREAK
         handler = lambda x, y: None
-        signal.signal(signal.SIGABRT, handler)
-        signal.signal(signal.SIGFPE, handler)
-        signal.signal(signal.SIGILL, handler)
-        signal.signal(signal.SIGINT, handler)
-        signal.signal(signal.SIGSEGV, handler)
-        signal.signal(signal.SIGTERM, handler)
+        for sig in (signal.SIGABRT, signal.SIGBREAK, signal.SIGFPE,
+                    signal.SIGILL, signal.SIGINT, signal.SIGSEGV,
+                    signal.SIGTERM):
+            # Set and then reset a handler for signals that work on windows
+            signal.signal(sig, signal.signal(sig, handler))
 
         with self.assertRaises(ValueError):
             signal.signal(-1, handler)
diff --git a/Misc/NEWS b/Misc/NEWS
index a0d8275..8e99376 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #10003: Allow handling of SIGBREAK on Windows. Fixes a regression
+  introduced by issue #9324. 
+
 - Issue #9979: Create function PyUnicode_AsWideCharString().
 
 - Issue #7397: Mention that importlib.import_module() is probably what someone
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index 8b60e41..d34e177 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -261,6 +261,11 @@
     /* Validate that sig_num is one of the allowable signals */
     switch (sig_num) {
         case SIGABRT: break;
+#ifdef SIGBREAK
+        /* Issue #10003: SIGBREAK is not documented as permitted, but works
+           and corresponds to CTRL_BREAK_EVENT. */
+        case SIGBREAK: break;
+#endif
         case SIGFPE: break;
         case SIGILL: break;
         case SIGINT: break;