base: Replace cppversion == version with >= version
base: Replace cppversion == version with >= version

For forward compatibility with later compilers, we should have a greater
than comparison instead of an explicit equality with a particular C++
version.

Change-Id: If848097420b9575f80134986410da3dab32567da
Signed-off-by: Bradley Wang <03def501f0fad14d746f73f57bce2ebf46787c45@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/11871
Reviewed-by: Jason Lowe-Power <68c46a606457643eab92053c1c05574abb26f861@lowepower.com>
Reviewed-by: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>
Reviewed-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Maintainer: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@google.com>

TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,gem5/gem5,gem5/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gem5/gem5,TUD-OS/gem5-dtu,gem5/gem5