scons: Add a target for google-perftools profiling
scons: Add a target for google-perftools profiling

This patch adds a new target called 'perf' that facilitates profiling
using google perftools rather than gprof. The perftools CPU profiler
offers plenty useful information in addition to gprof, and the latter
is kept mostly to offer profiling also on non-Linux hosts.

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