scons: Add tag support to ISADesc.
scons: Add tag support to ISADesc.

Change-Id: Icac027cc4df48d0a3c06911bd6fa0a8b5b72c60a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/50329
Reviewed-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5