There are ports of gcc available, but they only work on mint. And they are quite large, and slow compared to other compilers on the Atari, so i would not recommend using them natively on all but really fast hardware, like ct60 or firebee (i once compiled gcc by itself on Aranym with JIT, that took about 20h, the same task on linux takes 3min). gdb does not work anymore.
There are however cross-compilers available, for linux, windows and macos, from Vincent
(gcc 4.6.4), and from me
(also gcc 4.6.4, but also some newer versions,plus several libraries)