When we start to build gem5. We will read and process all of SConsopts files, and process the after_sconsopts_callbacks after all of SConsopts files read. In the KVM_ISA env setting, the KVM_ISA env can be set in the different files, take x86 and arm as example: KVM_ISA default value:bc39283451/src/cpu/kvm/SConsoptsx86 KVM_ISA:bc39283451/src/arch/x86/kvm/SConsopts (L39-L45)arm KVM_ISA:bc39283451/src/arch/arm/kvm/SConsopts (L35-L36)We should move the kvm warning after all of SConsopts env read issue: https://github.com/gem5/gem5/issues/686 Change-Id: I096c6bebaaec18f9b2af93191d0dd23c65084eda