Fwiw there's no real problem with gcc-specific code on FreeBSD if you're writing application software. Kernel code and core utilities in the base install are supposed to be able to compile with clang, but stuff in ports can use anything that is itself available in ports. The ports system makes it easy to specify when something requires gcc to compile vs. any C compiler, and doing so is fairly common (heck, it's not a problem to require even more exotic things either, like Ocaml or gfortran).