rt: Set Linux red zone to 20K again

With runtime logging on it smashes the stack

src/rt/rust_task.cpp

@@ -18,8 +18,8 @@
 // The amount of extra space at the end of each stack segment, available
 // to the rt, compiler and dynamic linker for running small functions
 // 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_LINUX_32 (1024*20)
+#define RZ_LINUX_64 (1024*20)
 #define RZ_MAC_32   (1024*20)
 #define RZ_MAC_64   (1024*20)
 #define RZ_WIN_32   (1024*20)