env_universal_common: always pick shmem strategy on Cygwin

Cygwin FIFOs do not support more than one reader, so avoid them on this
platform. An autoconf feature test would be helpful but is tricky to
write.

Closes #2152.

src/env_universal_common.cpp

@@ -1626,6 +1626,8 @@ universal_notifier_t::notifier_strategy_t universal_notifier_t::resolve_default_
     }
 #if FISH_NOTIFYD_AVAILABLE
     return strategy_notifyd;
+#elif defined(__CYGWIN__)
+    return strategy_shmem_polling;
 #else
     return strategy_named_pipe;
 #endif