website: Update supported GCC version to 11

GCC-11 was added to the compiler tests here:
https://gem5-review.googlesource.com/c/public/gem5/+/50749

Change-Id: If88769238619a32ad067e09fc38e39d4bcb0b915
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/50767
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
2 files changed