Don't use jit_State during build with JIT disabled.

src/lj_jit.h

@@ -7,6 +7,7 @@
 #define _LJ_JIT_H
 
 #include "lj_obj.h"
+#if LJ_HASJIT
 #include "lj_ir.h"
 
 /* -- JIT engine flags ---------------------------------------------------- */
@@ -516,5 +517,6 @@ typedef struct jit_State {
 #else
 #define lj_assertJ(c, ...)	((void)J)
 #endif
+#endif
 
 #endif