Use lj_vm_tobit() on targets without FPU.

src/lj_obj.h

@@ -786,11 +786,19 @@ static LJ_AINLINE void copyTV(lua_State *L, TValue *o1, const TValue *o2)
 
 /* -- Number to integer conversion ---------------------------------------- */
 
+#if !LJ_ARCH_HASFPU
+LJ_ASMF int32_t lj_vm_tobit(double x);
+#endif
+
 static LJ_AINLINE int32_t lj_num2bit(lua_Number n)
 {
+#if LJ_ARCH_HASFPU
   TValue o;
   o.n = n + 6755399441055744.0;  /* 2^52 + 2^51 */
   return (int32_t)o.u32.lo;
+#else
+  return lj_vm_tobit(n);
+#endif
 }
 
 #if LJ_TARGET_X86 && !defined(__SSE2__)