Use names defined in lualib.h for library registration.

src/lib_math.c

@@ -167,7 +167,7 @@ LUALIB_API int luaopen_math(lua_State *L)
   RandomState *rs;
   rs = (RandomState *)lua_newuserdata(L, sizeof(RandomState));
   rs->valid = 0;  /* Use lazy initialization to save some time on startup. */
-  LJ_LIB_REG(L, math);
+  LJ_LIB_REG(L, LUA_MATHLIBNAME, math);
 #if defined(LUA_COMPAT_MOD)
   lua_getfield(L, -1, "fmod");
   lua_setfield(L, -2, "mod");