Well, I didn't see the header files in any of the usual places:
/usr/include,
/usr/local/include
/usr/include/ncurses/
It's possible I overlooked it, but CMake find_package() couldn't locate ncurses either. All that being the case, I installed ncurses from source. I assume the duplicate definitions were coming from a header that Xcode provided for terminfo related functions. I reached that conclusion because all of the functions are terminfo related (tigetnum, tiparm, etc...).
Unfortunately, I won't have access to that system for a couple of days so I'll have to check again when I can.
Thanks!