[chapel-lang/chapel] Use a newer gcc for CS testing

Branch: refs/heads/master
Revision: 3639e1a
Author: ronawho
Log Message:

Merge pull request #16296 from ronawho/use-newer-gcc-cs-testing

Use a newer gcc for CS testing

The default gcc is 6.1, which is having problems with newer llvm
versions so bump to 8.1. I was thinking about only bumping llvm testing,
but 6.1 is getting old, so it’s probably worth using a newer version
across the board.

Modified Files:
M util/cron/common-cray-cs.bash

Compare: https://github.com/chapel-lang/chapel/compare/0dc602c0adf2...3639e1ab99eb