Revert "rt: Reduce mac red zone to 6K"

This reverts commit d499e73.

Author: brson

src/rt/rust_task.cpp

@@ -20,8 +20,8 @@
 // FIXME: We want this to be 128 but need to slim the red zone calls down
 #define RZ_LINUX_32 (1024*2)
 #define RZ_LINUX_64 (1024*2)
-#define RZ_MAC_32   (1024*6)
-#define RZ_MAC_64   (1024*6)
+#define RZ_MAC_32   (1024*20)
+#define RZ_MAC_64   (1024*20)
 #define RZ_WIN_32   (1024*20)
 #define RZ_BSD_32   (1024*20)
 #define RZ_BSD_64   (1024*20)