most people's Makefile only contains information for a Final Release and a Debug version of builds. You would want to clone the Debug information and rename it to Release (basically, just search for Debug, and everywhere you find one, copy that entire line, then go through it and change any Debug to a Release).
Once you have cloned debug, then change the flags to remove whatever it is you don't want from the debug DLL. Honestly though I can only think that you are seeking to reduce the size of the DLL, and it is enabling the Asserts which added the size to it in the first place, so I doubt that you will notice any difference in any other manner (Far as I can recall, debug only enables the Asserts and the Profiler, otherwise it is the same as the Final Release, so the only gain from creating a Release build would be to disable the profiler while still enabling the Asserts, which is exactly backwards of what Release normally is used for (ie - normally it is used to disable the asserts, but retain the profiler for final checking of performance). I haven't done "pro" work though, so I can't say for certain)