cygthread: suspend thread before terminating.

It seems SuspendThread makes sure the thread is "booted" from emulation
before it is suspended.  Hopefully this means it won't be holding any
locks or otherwise leave emulation in a bad state when it's terminated.

Addresses: https://cygwin.com/pipermail/cygwin-developers/2024-May/012694.html
Signed-off-by: Jeremy Drake <cygwin@jdrake.com>

winsup/cygwin/cygthread.cc

@@ -302,6 +302,20 @@ cygthread::terminate_thread ()
   if (!inuse)
     goto force_notterminated;
 
+  if (_my_tls._ctinfo != this)
+    {
+      CONTEXT context;
+      context.ContextFlags = CONTEXT_CONTROL;
+      /* SuspendThread makes sure a thread is "booted" from emulation before
+         it is suspended.  As such, the emulator hopefully won't be in a bad
+	 state (aka, holding any locks) when the thread is terminated. */
+      SuspendThread (h);
+      /* We need to call GetThreadContext, even though we don't care about the
+         context, because SuspendThread is asynchronous and GetThreadContext
+         will make sure the thread is *really* suspended before returning */
+      GetThreadContext (h, &context);
+    }
+
   TerminateThread (h, 0);
   WaitForSingleObject (h, INFINITE);
   CloseHandle (h);