Fix rotate definitions for variable shifts.

src/lj_def.h

@@ -101,8 +101,8 @@ typedef unsigned int uintptr_t;
 #define checkptr32(x)	((uintptr_t)(x) == (uint32_t)(uintptr_t)(x))
 
 /* Every half-decent C compiler transforms this into a rotate instruction. */
-#define lj_rol(x, n)	(((x)<<(n)) | ((x)>>(8*sizeof(x)-(n))))
-#define lj_ror(x, n)	(((x)<<(8*sizeof(x)-(n))) | ((x)>>(n)))
+#define lj_rol(x, n)	(((x)<<(n)) | ((x)>>(-(int)(n)&(8*sizeof(x)-1))))
+#define lj_ror(x, n)	(((x)<<(-(int)(n)&(8*sizeof(x)-1))) | ((x)>>(n)))
 
 /* A really naive Bloom filter. But sufficient for our needs. */
 typedef uintptr_t BloomFilter;