I use ctags with vim and the OmniCppComplete plugin. Currently when generating my tags I do it individually for each library. For libc6 I use the following list of tokens
Sorry--I've never used ctags before--but I'll take a stab at this question.
If I understand correctly, you can use the list of keywords from GCC itself. I found this https://gist.github.com/959484 inside gcc/gcc/c-family/c-common.c. Looks like it includes reserved words for all the C (c/c++/obj-c variants). I guess some are valid for all compilers, these are for gcc of course.
As for figuring out other symbols to ignore, on OS X I'd use nm to dump the symbols of the library in question an add all symbols marked as private ('s' instead of 'S' for example) to my list of symbols to ignore. Linux has a similar library-dumping tool?
Hope that's useful.