UPDATE ON PROGRESS/FINDINGS:
(I apologize for the double post, but I do not know how to indicate that this is still being worked on otherwise. just editing a post will not flag a topic as having new content. sorry!
When searching around the internet for solutions to the problem of the _main symbol being undefined, one person somewhere suggested that the files in question should be pre-processed and the output of that should be looked at. So I added the -save-temps flag to the build.flags file, to get the pre-processed output and poke around in it. Turns out, the main function does not exist anywhere within the processed files, and only SDL_main can be found.
My current theory is that SDLmain.m/h are not being included in the makefile, and are thus not being built, which is why main can't be found. Unfortunately, Objective-C is a type of mysticism to me right now, and I do not know how to make it be included in the makefile and have it built. I will continue investigating this, and will be checking the pre-made XCode projects that SDL provides to see how it is accomplished there.
I will make another post (possibly) when I have more progress to report, or if I manage to fix the problem. If anybody knows how to get SDLmain.m/h included during the build process, please let me know, as that could save me a lot of trouble. I'll be checking back into the forum for a few hours today as I work on this.