misc,tests: Remove support for GCC 6

Supporting GCC 7 onwards will allow us to move to the C++17 standard.

Change-Id: I805945230d77dacdc6b0a863153b28276025ecdc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47460
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed