There is absolutely no need to even involve chroots or anything that needs special privilege just to run a compiler. Typically, a compiler will just read and write files. This is how it ought to work.

  1. Download gcc-8.x.y.tar.xz
  2. Untar anywhere.  I like to do this within my home directory.
  3. Run ~/stuff/gcc-8.x.y/bin/gcc

If this simplest possible thing does not work and drives you to Docker or chroots or similar things, then something fundamental is broken.