Compiling gem5 with systemc enabled results in the errors described in https://gem5.atlassian.net/browse/GEM5-1027. This change tells scons not to compile gem5 with systemc when the host ISA is RISC-V. JIRA: https://gem5.atlassian.net/browse/GEM5-1027 Change-Id: I04e1bc722c9d702472152c9116d89938e8408047 Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu> Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47660 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Reviewed-by: Gabe Black <gabe.black@gmail.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>