Do not use CMake CONCAT
Do not use CMake CONCAT

CONCAT was added quite late in the CMake release cycles so lets use `set()`
instead which has been around _forever_...

xlqian/benchmark,subailong/benchmark,chemhack/benchmark,ntx-/benchmark,nickhutchinson/benchmark,gezidan/benchmark,LepelTsmok/benchmark,disconnect3d/benchmark,LepelTsmok/benchmark,Photonomie/benchmark,codygray/benchmark,subailong/benchmark,gezidan/benchmark,codygray/benchmark,nickhutchinson/benchmark-cxx03,nickhutchinson/benchmark-cxx03,chemhack/benchmark,fuchsia-mirror/third_party-benchmark,everbase/benchmark,efcs/benchmark,eliben/benchmark,quantumsteve/benchmark,quantumsteve/benchmark,xlqian/benchmark,disconnect3d/benchmark,mockingbirdnest/benchmark,xlqian/benchmark,codygray/benchmark,nickhutchinson/benchmark,chandlerc/benchmark,Photonomie/benchmark,Photonomie/benchmark,everbase/benchmark,LepelTsmok/benchmark,efcs/benchmark,disconnect3d/benchmark,bowlofstew/benchmark,chemhack/benchmark,fuchsia-mirror/third_party-benchmark,fuchsia-mirror/third_party-benchmark,xlqian/benchmark,bowlofstew/benchmark,nickhutchinson/benchmark-cxx03,everbase/benchmark,gezidan/benchmark,mockingbirdnest/benchmark,nickhutchinson/benchmark,quantumsteve/benchmark,everbase/benchmark,chemhack/benchmark,bowlofstew/benchmark,nickhutchinson/benchmark-cxx03,Photonomie/benchmark,disconnect3d/benchmark,eliben/benchmark,google/benchmark,subailong/benchmark,eliben/benchmark,subailong/benchmark,codygray/benchmark,gezidan/benchmark,mockingbirdnest/benchmark,chandlerc/benchmark,eliben/benchmark,LepelTsmok/benchmark,ntx-/benchmark,google/benchmark,mockingbirdnest/benchmark,ntx-/benchmark,chandlerc/benchmark,ntx-/benchmark,fuchsia-mirror/third_party-benchmark,chandlerc/benchmark,quantumsteve/benchmark,google/benchmark,efcs/benchmark,bowlofstew/benchmark,efcs/benchmark,nickhutchinson/benchmark