[runtime] Ignore SIGPIPE for watchOS.

Usually mono does this for other apps, but not for watchOS (where mono doesn't
use signals at all).

watchOS can still raise signals though, so we need to ignore at least SIGPIPE.

runtime/monotouch-main.m

@@ -254,6 +254,11 @@ xamarin_main (int argc, char *argv[], bool is_extension)
 	setenv ("DYLD_BIND_AT_LAUNCH", "1", 1);
 	setenv ("MONO_REFLECTION_SERIALIZER", "yes", 1);
 
+#if TARGET_OS_WATCH
+	// watchOS can raise signals just fine...
+	// we might want to move this inside mono at some point.
+	signal (SIGPIPE, SIG_IGN);
+#endif
 
 #if TARGET_OS_WATCH || TARGET_OS_TV
 	mini_parse_debug_option ("explicit-null-checks");