util,tests: Removed GCC 4.8 from compilers tests

util,tests: Removed GCC 4.8 from compilers tests

We are going to remove support of GCC 4
(https://gem5.atlassian.net/browse/GEM5-218) as part of the gem5 20.1
release.

Change-Id: Ie44b553d35f48118d24b96eba564a927fefdb985
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32096
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>