[runtime] Re-enable the gc pump by default for debug simulator/mac builds. (#50)

runtime/runtime.m

@@ -35,7 +35,11 @@ bool xamarin_detect_unified_build = true;
 bool xamarin_detect_unified_build = false;
 #endif
 bool xamarin_use_new_assemblies = false;
+#if DEBUG && (defined (__i386__) || defined (__x86_64__))
+bool xamarin_gc_pump = true;
+#else
 bool xamarin_gc_pump = false;
+#endif
 #if MONOMAC
 // FIXME: implement release mode for monomac.
 bool xamarin_debug_mode = true;