python: fix m5.build_env variable. As it is now, some objects will get the incorrect value depending where they were defined.
python: fix m5.build_env variable.
As it is now, some objects will get the incorrect value depending where they
were defined.

--HG--
extra : convert_revision : a11a14842f9524739cbf54a48be6ec051f371200

austinharris/gem5-riscv,samueldotj/TeeRISC-Simulator,joerocklin/gem5,kaiyuanl/gem5,aclifton/cpeg853-gem5,rjschof/gem5,TUD-OS/gem5-dtu,SanchayanMaity/gem5,joerocklin/gem5,gedare/gem5,Weil0ng/gem5,joerocklin/gem5,powerjg/gem5-ci-test,briancoutinho0905/2dsampling,samueldotj/TeeRISC-Simulator,cancro7/gem5,SanchayanMaity/gem5,gem5/gem5,aclifton/cpeg853-gem5,SanchayanMaity/gem5,austinharris/gem5-riscv,rallylee/gem5,yb-kim/gemV,cancro7/gem5,rallylee/gem5,powerjg/gem5-ci-test,briancoutinho0905/2dsampling,SanchayanMaity/gem5,TUD-OS/gem5-dtu,HwisooSo/gemV-update,kaiyuanl/gem5,aclifton/cpeg853-gem5,zlfben/gem5,cancro7/gem5,KuroeKurose/gem5,zlfben/gem5,HwisooSo/gemV-update,yb-kim/gemV,gedare/gem5,Weil0ng/gem5,gedare/gem5,qizenguf/MLC-STT,austinharris/gem5-riscv,rallylee/gem5,markoshorro/gem5,qizenguf/MLC-STT,aclifton/cpeg853-gem5,aclifton/cpeg853-gem5,briancoutinho0905/2dsampling,zlfben/gem5,austinharris/gem5-riscv,KuroeKurose/gem5,SanchayanMaity/gem5,cancro7/gem5,sobercoder/gem5,aclifton/cpeg853-gem5,sobercoder/gem5,samueldotj/TeeRISC-Simulator,briancoutinho0905/2dsampling,markoshorro/gem5,gedare/gem5,markoshorro/gem5,Weil0ng/gem5,qizenguf/MLC-STT,joerocklin/gem5,yb-kim/gemV,qizenguf/MLC-STT,briancoutinho0905/2dsampling,austinharris/gem5-riscv,yb-kim/gemV,cancro7/gem5,qizenguf/MLC-STT,gedare/gem5,rallylee/gem5,austinharris/gem5-riscv,markoshorro/gem5,TUD-OS/gem5-dtu,gem5/gem5,powerjg/gem5-ci-test,samueldotj/TeeRISC-Simulator,qizenguf/MLC-STT,powerjg/gem5-ci-test,zlfben/gem5,KuroeKurose/gem5,KuroeKurose/gem5,SanchayanMaity/gem5,kaiyuanl/gem5,samueldotj/TeeRISC-Simulator,gem5/gem5,yb-kim/gemV,HwisooSo/gemV-update,sobercoder/gem5,kaiyuanl/gem5,gem5/gem5,joerocklin/gem5,rjschof/gem5,kaiyuanl/gem5,markoshorro/gem5,TUD-OS/gem5-dtu,zlfben/gem5,TUD-OS/gem5-dtu,gedare/gem5,Weil0ng/gem5,kaiyuanl/gem5,Weil0ng/gem5,powerjg/gem5-ci-test,sobercoder/gem5,austinharris/gem5-riscv,HwisooSo/gemV-update,zlfben/gem5,gem5/gem5,yb-kim/gemV,aclifton/cpeg853-gem5,sobercoder/gem5,briancoutinho0905/2dsampling,HwisooSo/gemV-update,sobercoder/gem5,gem5/gem5,joerocklin/gem5,Weil0ng/gem5,gedare/gem5,yb-kim/gemV,samueldotj/TeeRISC-Simulator,cancro7/gem5,KuroeKurose/gem5,rallylee/gem5,yb-kim/gemV,HwisooSo/gemV-update,sobercoder/gem5,powerjg/gem5-ci-test,TUD-OS/gem5-dtu,HwisooSo/gemV-update,markoshorro/gem5,SanchayanMaity/gem5,rallylee/gem5,Weil0ng/gem5,TUD-OS/gem5-dtu,briancoutinho0905/2dsampling,rjschof/gem5,kaiyuanl/gem5,KuroeKurose/gem5,rjschof/gem5,samueldotj/TeeRISC-Simulator,joerocklin/gem5,zlfben/gem5,joerocklin/gem5,rjschof/gem5,cancro7/gem5,qizenguf/MLC-STT,KuroeKurose/gem5,markoshorro/gem5,rjschof/gem5,rjschof/gem5,powerjg/gem5-ci-test,rallylee/gem5,gem5/gem5