scons: When importing SimObjects, use a copy of globals().
scons: When importing SimObjects, use a copy of globals().

Use a copy of globals when importing SimObjects, instead of the real
deal that the SConscript runs under. This avoids polluting the
SConscript namespace.

Change-Id: I689d693d93cc8998be0967ec2b0c58f5851d39cf
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49407
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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