Simplify implementation of GetProcessorCount().
Simplify implementation of GetProcessorCount().

The current implementation is unnecessarily complex, because:

- The BSD derived systems implement sysconf(_SC_NPROCESSORS_ONLN)
  in terms of sysctl({CTL_HW,HW_NCPU}).
- get_nprocs() is a GNU extension, and glibc implements
  sysconf(_SC_NPROCESSORS_ONLN) in terms of get_nprocs().

nicolasdespres/ninja,drbo/ninja,purcell/ninja,sorbits/ninja,dorgonman/ninja,jimon/ninja,nico/ninja,Qix-/ninja,tfarina/ninja,ThiagoGarciaAlves/ninja,ndsol/subninja,glensc/ninja,hnney/ninja,drbo/ninja,ignatenkobrain/ninja,metti/ninja,mgaunard/ninja,fuchsia-mirror/third_party-ninja,vvvrrooomm/ninja,vvvrrooomm/ninja,mydongistiny/ninja,nafest/ninja,lizh06/ninja,fifoforlifo/ninja,ThiagoGarciaAlves/ninja,colincross/ninja,guiquanz/ninja,bradking/ninja,glensc/ninja,ninja-build/ninja,sgraham/ninja,metti/ninja,sorbits/ninja,kissthink/ninja,drbo/ninja,jhanssen/ninja,synaptek/ninja,colincross/ninja,ndsol/subninja,lizh06/ninja,Qix-/ninja,purcell/ninja,hnney/ninja,ndsol/subninja,fifoforlifo/ninja,fuchsia-mirror/third_party-ninja,nicolasdespres/ninja,ilor/ninja,Maratyszcza/ninja-pypi,mohamed/ninja,fuchsia-mirror/third_party-ninja,sxlin/dist_ninja,metti/ninja,mgaunard/ninja,sxlin/dist_ninja,nocnokneo/ninja,autopulated/ninja,syntheticpp/ninja,juntalis/ninja,juntalis/ninja,hnney/ninja,martine/ninja,sgraham/ninja,nocnokneo/ninja,dorgonman/ninja,ignatenkobrain/ninja,glensc/ninja,Qix-/ninja,Ju2ender/ninja,mohamed/ninja,mydongistiny/ninja,mgaunard/ninja,colincross/ninja,jhanssen/ninja,dorgonman/ninja,nicolasdespres/ninja,guiquanz/ninja,ilor/ninja,drbo/ninja,nickhutchinson/ninja,ignatenkobrain/ninja,rjogrady/ninja,tfarina/ninja,dendy/ninja,jendrikillner/ninja,bmeurer/ninja,ignatenkobrain/ninja,nickhutchinson/ninja,maruel/ninja,dendy/ninja,sgraham/ninja,autopulated/ninja,ilor/ninja,mydongistiny/ninja,nicolasdespres/ninja,nafest/ninja,nafest/ninja,AoD314/ninja,kissthink/ninja,ctiller/ninja,martine/ninja,vvvrrooomm/ninja,rjogrady/ninja,dendy/ninja,fuchsia-mirror/third_party-ninja,iwadon/ninja,atetubou/ninja,nafest/ninja,kissthink/ninja,autopulated/ninja,sxlin/dist_ninja,bradking/ninja,sgraham/ninja,tfarina/ninja,vvvrrooomm/ninja,automeka/ninja,fifoforlifo/ninja,sxlin/dist_ninja,glensc/ninja,dpwright/ninja,metti/ninja,bradking/ninja,moroten/ninja,atetubou/ninja,ilor/ninja,lizh06/ninja,jimon/ninja,automeka/ninja,rjogrady/ninja,tfarina/ninja,lizh06/ninja,mgaunard/ninja,synaptek/ninja,Maratyszcza/ninja-pypi,bradking/ninja,Ju2ender/ninja,iwadon/ninja,atetubou/ninja,nocnokneo/ninja,guiquanz/ninja,mohamed/ninja,syntheticpp/ninja,ninja-build/ninja,synaptek/ninja,liukd/ninja,ninja-build/ninja,liukd/ninja,AoD314/ninja,juntalis/ninja,synaptek/ninja,fifoforlifo/ninja,martine/ninja,jendrikillner/ninja,atetubou/ninja,automeka/ninja,ThiagoGarciaAlves/ninja,maruel/ninja,liukd/ninja,jhanssen/ninja,moroten/ninja,mydongistiny/ninja,ndsol/subninja,hnney/ninja,Maratyszcza/ninja-pypi,dpwright/ninja,nocnokneo/ninja,Ju2ender/ninja,kissthink/ninja,purcell/ninja,autopulated/ninja,liukd/ninja,automeka/ninja,moroten/ninja,AoD314/ninja,ninja-build/ninja,nico/ninja,sxlin/dist_ninja,iwadon/ninja,dorgonman/ninja,ctiller/ninja,dpwright/ninja,nico/ninja,nickhutchinson/ninja,dendy/ninja,mohamed/ninja,ThiagoGarciaAlves/ninja,colincross/ninja,Qix-/ninja,jimon/ninja,moroten/ninja,ctiller/ninja,guiquanz/ninja,syntheticpp/ninja,dpwright/ninja,maruel/ninja,maruel/ninja,sorbits/ninja,rjogrady/ninja,jimon/ninja,jendrikillner/ninja,jhanssen/ninja,bmeurer/ninja,ctiller/ninja,Maratyszcza/ninja-pypi,AoD314/ninja,sxlin/dist_ninja,bmeurer/ninja,Ju2ender/ninja,martine/ninja,juntalis/ninja,nickhutchinson/ninja,jendrikillner/ninja,sorbits/ninja,iwadon/ninja,purcell/ninja,sxlin/dist_ninja,syntheticpp/ninja,nico/ninja,bmeurer/ninja