rt: Parenthesize the red zone macros

Author: brson

src/rt/rust_task.cpp

@@ -18,11 +18,11 @@
 // 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*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
+#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)
 
 #ifdef __linux__
 #ifdef __i386__