Fix warning when compiling for m68k

* syscall.c (d0): Define as long.
diff --git a/syscall.c b/syscall.c
index b7bb733..40eee3a 100644
--- a/syscall.c
+++ b/syscall.c
@@ -727,7 +727,7 @@
 #elif defined (POWERPC)
 	static long result,flags;
 #elif defined (M68K)
-	static int d0;
+	static long d0;
 #elif defined(BFIN)
 	static long r0;
 #elif defined (ARM)