julia: 1.2.0 -> 1.4.1 update
- Run julia and check that the mandelbrot code from https://julialang.org/learning/code-examples/ works
- Delete ~/.julia/ and enter julia REPL pkg mode and update packages successfully
- Build with GCC instead of clang (julia needs to use its own patched LLVM).
- Use system zlib
- Do not attempt to do a parallel install (force -j1)