Add extra debug information when failing to deliver an interrupt message.

runtime/bin/eventhandler_macos.cc

Index: runtime/bin/eventhandler_macos.cc
diff --git a/runtime/bin/eventhandler_macos.cc b/runtime/bin/eventhandler_macos.cc
index 2e2ad9d5c07d71e47876181281a5d3b6d4f6affb..d4aa0841d422d6c0838005a2dec1e4f1b1754fb4 100644
--- a/runtime/bin/eventhandler_macos.cc
+++ b/runtime/bin/eventhandler_macos.cc
@@ -95,7 +95,10 @@ void EventHandlerImplementation::WakeupHandler(intptr_t id,
   intptr_t result =
       FDUtils::WriteToBlocking(interrupt_fds_[1], &msg, kInterruptMessageSize);
   if (result != kInterruptMessageSize) {
-    FATAL("Interrupt message failure");
+    if (result == -1) {
+      perror("Interrupt message failure:");
+    }
+    FATAL1("Interrupt message failure. Wrote %d bytes.", result);
   }
 }