don't leak the build_log file descriptor into subprocesses
don't leak the build_log file descriptor into subprocesses

Closes issue #74.

colincross/ninja,purcell/ninja,mutac/ninja,yannicklm/ninja,tychoish/ninja,colincross/ninja,chenyukang/ninja,PetrWolf/ninja-main,TheOneRing/ninja,jendrikillner/ninja,TheOneRing/ninja,colincross/ninja,lizh06/ninja,hnney/ninja,rnk/ninja,automeka/ninja,nornagon/ninja,dpwright/ninja,mutac/ninja,SByer/ninja,dpwright/ninja,mdempsky/ninja,mathstuf/ninja,fuchsia-mirror/third_party-ninja,nickhutchinson/ninja,ThiagoGarciaAlves/ninja,dorgonman/ninja,sxlin/dist_ninja,sxlin/dist_ninja,glensc/ninja,atetubou/ninja,nornagon/ninja,nico/ninja,jimon/ninja,tychoish/ninja,mohamed/ninja,autopulated/ninja,fifoforlifo/ninja,kissthink/ninja,ndsol/subninja,liukd/ninja,cipriancraciun/ninja,rnk/ninja,tychoish/ninja,SByer/ninja,metti/ninja,Qix-/ninja,moroten/ninja,fuchsia-mirror/third_party-ninja,ukai/ninja,PetrWolf/ninja,ndsol/subninja,nornagon/ninja,martine/ninja,PetrWolf/ninja-main,barak/ninja,jendrikillner/ninja,fuchsia-mirror/third_party-ninja,sgraham/ninja,PetrWolf/ninja,vvvrrooomm/ninja,nafest/ninja,sgraham/ninja,ukai/ninja,sxlin/dist_ninja,yannicklm/ninja,sorbits/ninja,tfarina/ninja,ikarienator/ninja,jimon/ninja,mutac/ninja,sgraham/ninja,iwadon/ninja,Qix-/ninja,rnk/ninja,kissthink/ninja,glensc/ninja,purcell/ninja,bradking/ninja,ikarienator/ninja,mydongistiny/ninja,drbo/ninja,mydongistiny/ninja,nocnokneo/ninja,PetrWolf/ninja,mathstuf/ninja,hnney/ninja,ehird/ninja,LuaDist/ninja,barak/ninja,automeka/ninja,vvvrrooomm/ninja,fifoforlifo/ninja,martine/ninja,kissthink/ninja,TheOneRing/ninja,dabrahams/ninja,nicolasdespres/ninja,moroten/ninja,kissthink/ninja,LuaDist/ninja,ehird/ninja,juntalis/ninja,Maratyszcza/ninja-pypi,iwadon/ninja,ThiagoGarciaAlves/ninja,ninja-build/ninja,mdempsky/ninja,barak/ninja,nafest/ninja,guiquanz/ninja,ninja-build/ninja,mydongistiny/ninja,bmeurer/ninja,Ju2ender/ninja,jhanssen/ninja,ilor/ninja,bmeurer/ninja,PetrWolf/ninja-main,dabrahams/ninja,SByer/ninja,dpwright/ninja,ignatenkobrain/ninja,juntalis/ninja,LuaDist/ninja,chenyukang/ninja,mohamed/ninja,rjogrady/ninja,dorgonman/ninja,fifoforlifo/ninja,mutac/ninja,nico/ninja,lizh06/ninja,jsternberg/ninja,ignatenkobrain/ninja,ThiagoGarciaAlves/ninja,martine/ninja,PetrWolf/ninja,guiquanz/ninja,martine/ninja,mohamed/ninja,okuoku/ninja,maximuska/ninja,pcc/ninja,cipriancraciun/ninja,sxlin/dist_ninja,liukd/ninja,ninja-build/ninja,bmeurer/ninja,ctiller/ninja,yannicklm/ninja,bradking/ninja,ikarienator/ninja,sorbits/ninja,pck/ninja,dabrahams/ninja,chenyukang/ninja,mgaunard/ninja,ilor/ninja,Maratyszcza/ninja-pypi,pck/ninja,mdempsky/ninja,synaptek/ninja,nicolasdespres/ninja,okuoku/ninja,maximuska/ninja,AoD314/ninja,nico/ninja,sgraham/ninja,tfarina/ninja,nornagon/ninja,synaptek/ninja,syntheticpp/ninja,nico/ninja,glensc/ninja,maruel/ninja,bradking/ninja,chenyukang/ninja,ikarienator/ninja,hnney/ninja,curinir/ninja,pathscale/ninja,syntheticpp/ninja,nafest/ninja,iwadon/ninja,bmeurer/ninja,curinir/ninja,fuchsia-mirror/third_party-ninja,nickhutchinson/ninja,ukai/ninja,Maratyszcza/ninja-pypi,juntalis/ninja,maruel/ninja,PetrWolf/ninja-main,atetubou/ninja,purcell/ninja,ilor/ninja,mdempsky/ninja,okuoku/ninja,nafest/ninja,maximuska/ninja,jsternberg/ninja,dpwright/ninja,jendrikillner/ninja,jhanssen/ninja,nocnokneo/ninja,AoD314/ninja,AoD314/ninja,maruel/ninja,metti/ninja,synaptek/ninja,mohamed/ninja,mathstuf/ninja,Ju2ender/ninja,kimgr/ninja,ndsol/subninja,automeka/ninja,purcell/ninja,mgaunard/ninja,okuoku/ninja,dorgonman/ninja,nicolasdespres/ninja,AoD314/ninja,Qix-/ninja,ThiagoGarciaAlves/ninja,cipriancraciun/ninja,liukd/ninja,ndsol/subninja,sxlin/dist_ninja,mgaunard/ninja,tfarina/ninja,autopulated/ninja,TheOneRing/ninja,jimon/ninja,jhanssen/ninja,tfarina/ninja,syntheticpp/ninja,Ju2ender/ninja,pcc/ninja,ninja-build/ninja,SByer/ninja,ignatenkobrain/ninja,curinir/ninja,atetubou/ninja,fifoforlifo/ninja,guiquanz/ninja,ctiller/ninja,kimgr/ninja,ilor/ninja,sorbits/ninja,liukd/ninja,LuaDist/ninja,glensc/ninja,nocnokneo/ninja,mydongistiny/ninja,ehird/ninja,maruel/ninja,moroten/ninja,dabrahams/ninja,nocnokneo/ninja,rjogrady/ninja,drbo/ninja,vvvrrooomm/ninja,atetubou/ninja,mgaunard/ninja,pck/ninja,pathscale/ninja,cipriancraciun/ninja,yannicklm/ninja,moroten/ninja,autopulated/ninja,kimgr/ninja,drbo/ninja,jendrikillner/ninja,curinir/ninja,dendy/ninja,rjogrady/ninja,ukai/ninja,metti/ninja,hnney/ninja,mathstuf/ninja,pcc/ninja,jsternberg/ninja,ctiller/ninja,pathscale/ninja,Qix-/ninja,pck/ninja,ctiller/ninja,iwadon/ninja,lizh06/ninja,sxlin/dist_ninja,synaptek/ninja,Maratyszcza/ninja-pypi,autopulated/ninja,sorbits/ninja,juntalis/ninja,maximuska/ninja,ignatenkobrain/ninja,jhanssen/ninja,colincross/ninja,automeka/ninja,jsternberg/ninja,dendy/ninja,dorgonman/ninja,vvvrrooomm/ninja,guiquanz/ninja,jimon/ninja,barak/ninja,tychoish/ninja,Ju2ender/ninja,pcc/ninja,rnk/ninja,sxlin/dist_ninja,nicolasdespres/ninja,rjogrady/ninja,ehird/ninja,dendy/ninja,drbo/ninja,pathscale/ninja,nickhutchinson/ninja,syntheticpp/ninja,lizh06/ninja,bradking/ninja,dendy/ninja,kimgr/ninja,metti/ninja,nickhutchinson/ninja