Just enable hack on macOS

This is not needed on linux at all! Tried to explain as much as I
understand with the problem.

src/libmain/shared.cc

@@ -125,8 +125,14 @@ void initNix()
     act.sa_handler = sigHandler;
     if (sigaction(SIGUSR1, &act, 0)) throw SysError("handling SIGUSR1");
 
-    /* Make sure SIGWINCH is handled as well. */
-    if (sigaction(SIGWINCH, &act, 0)) throw SysError("handling SIGWINCH");
+#ifdef __APPLE__
+    /* HACK: on darwin, we need can’t use sigprocmask with SIGWINCH.
+     * Instead, add a dummy sigaction handler, and signalHandlerThread
+     * can handle the rest. */
+    struct sigaction sa;
+    sa.sa_handler = sigHandler;
+    if (sigaction(SIGWINCH, &sa, 0)) throw SysError("handling SIGWINCH");
+#endif
 
     /* Register a SIGSEGV handler to detect stack overflows. */
     detectStackOverflow();