If you are building on a Debian system you can optionally skip this section. One of the frequent problems in building gcc is getting the necessary prerequisites, fortunately there is a script in the source tree which will do this for you and the build process will automatically build these before the main gcc build. This build is all local.
It is worth reading https://gcc.gnu.org/wiki/InstallingGCC to make sure you have the various support libraries. To summarize it is probably safer to download the tarball and then the source for the prerequites as follows:
$ wget http://floppsie.comp.glam.ac.uk/download/c/gcc-8.2.0+gm2-git-latest.tar.gz $ tar zxf gcc-8.2.0+gm2-git-latest.tar.gz $ cd gcc-8.2.0+gm2-git-latest/gm2/gcc-versionno $ ./contrib/download_prerequisites $ cd ../../..
You can now move to the configure step in the next section.