Fixes compilation issue on Macs
Fixes compilation issue on Macs

ba141ac0d9f2 renamed OS_MACOSX -> BENCHMARK_OS_MACOSX,
except for an include guard in src/cycleclock.h

efcs/benchmark,eliben/benchmark,nickhutchinson/benchmark-cxx03,xlqian/benchmark,eliben/benchmark,ntx-/benchmark,eliben/benchmark,everbase/benchmark,nickhutchinson/benchmark-cxx03,chemhack/benchmark,nickhutchinson/benchmark,LepelTsmok/benchmark,codygray/benchmark,LepelTsmok/benchmark,everbase/benchmark,efcs/benchmark,chemhack/benchmark,nickhutchinson/benchmark,everbase/benchmark,mockingbirdnest/benchmark,google/benchmark,ntx-/benchmark,codygray/benchmark,xlqian/benchmark,chemhack/benchmark,disconnect3d/benchmark,codygray/benchmark,disconnect3d/benchmark,efcs/benchmark,nickhutchinson/benchmark-cxx03,mockingbirdnest/benchmark,everbase/benchmark,LepelTsmok/benchmark,google/benchmark,chemhack/benchmark,LepelTsmok/benchmark,nickhutchinson/benchmark,eliben/benchmark,mockingbirdnest/benchmark,fuchsia-mirror/third_party-benchmark,disconnect3d/benchmark,disconnect3d/benchmark,xlqian/benchmark,fuchsia-mirror/third_party-benchmark,ntx-/benchmark,fuchsia-mirror/third_party-benchmark,xlqian/benchmark,google/benchmark,nickhutchinson/benchmark-cxx03,fuchsia-mirror/third_party-benchmark,nickhutchinson/benchmark,mockingbirdnest/benchmark,efcs/benchmark,codygray/benchmark,ntx-/benchmark