Okay I am 100% sure this one will solve your problems because I was able to reproduce your exact error.
Am I correct that you downloaded SDL from libsdl.org and that is the copy you are using? If so, go back to the folder that the SDL distribution came in. Go to the /lib/ directory in that very SDL folder. Cut and copy "libSDLmain.a" and paste it into C:\Dev-C++\lib\. Now, add "-lsdlmain" *RIGHT BEFORE* (and it must be the only command that is right before) where it says "-lsdl" in the Linker Options area of the Project Options window (where you have been before). Compile, and this should fix it as it fixed it for me.
If you got your SDL from the Dev-C++ update thing and you installed that very package (don't get multiple packages confused), tell me. However, please make sure it is that very package that you got from that very Dev-C++ update manager. If you are sure it is, then try the above libSDLmain.a thing anyway. That still will probably fix it.
If you don't have libSDLmain.a for whatever reason, redownload the package you originally had and extract it.
This will fix it for sure this time. If you get a segfault when you run the compiled product, rebuild all of bzflag.dev because there are probably version problems amongst files. Now that I know for sure will work as I have done that hundreds of times