Use a different sentinel value to lock the free list.
Use a different sentinel value to lock the free list.

We're going to use null to indicate that the final GC has already
occurred.

rnestler/servo,eddyb/servo,KiChjang/servo,fiji-flo/servo,rnestler/servo,upsuper/servo,splav/servo,KiChjang/servo,dsandeephegde/servo,emilio/servo,splav/servo,splav/servo,peterjoel/servo,cbrewster/servo,nnethercote/servo,ConnorGBrewster/servo,saneyuki/servo,DominoTree/servo,upsuper/servo,rnestler/servo,canaltinova/servo,canaltinova/servo,mbrubeck/servo,jimberlage/servo,ConnorGBrewster/servo,dati91/servo,mbrubeck/servo,paulrouget/servo,szeged/servo,mbrubeck/servo,canaltinova/servo,jimberlage/servo,dati91/servo,ConnorGBrewster/servo,rnestler/servo,saneyuki/servo,DominoTree/servo,sadmansk/servo,szeged/servo,anthgur/servo,jimberlage/servo,paulrouget/servo,pyfisch/servo,upsuper/servo,avadacatavra/servo,pyfisch/servo,szeged/servo,KiChjang/servo,nnethercote/servo,pyfisch/servo,DominoTree/servo,DominoTree/servo,paulrouget/servo,pyfisch/servo,notriddle/servo,paulrouget/servo,DominoTree/servo,cbrewster/servo,fiji-flo/servo,notriddle/servo,KiChjang/servo,dsandeephegde/servo,sadmansk/servo,splav/servo,eddyb/servo,KiChjang/servo,eddyb/servo,anthgur/servo,cbrewster/servo,DominoTree/servo,SimonSapin/servo,SimonSapin/servo,mbrubeck/servo,mattnenterprise/servo,avadacatavra/servo,splav/servo,splav/servo,ConnorGBrewster/servo,nnethercote/servo,emilio/servo,anthgur/servo,mbrubeck/servo,eddyb/servo,DominoTree/servo,emilio/servo,mattnenterprise/servo,fiji-flo/servo,peterjoel/servo,emilio/servo,notriddle/servo,upsuper/servo,SimonSapin/servo,anthgur/servo,anthgur/servo,avadacatavra/servo,SimonSapin/servo,splav/servo,larsbergstrom/servo,cbrewster/servo,larsbergstrom/servo,fiji-flo/servo,rnestler/servo,mattnenterprise/servo,CJ8664/servo,notriddle/servo,larsbergstrom/servo,upsuper/servo,thiagopnts/servo,emilio/servo,paulrouget/servo,thiagopnts/servo,cbrewster/servo,canaltinova/servo,jimberlage/servo,peterjoel/servo,saneyuki/servo,szeged/servo,larsbergstrom/servo,paulrouget/servo,sadmansk/servo,mattnenterprise/servo,anthgur/servo,CJ8664/servo,dsandeephegde/servo,dati91/servo,larsbergstrom/servo,KiChjang/servo,SimonSapin/servo,notriddle/servo,szeged/servo,peterjoel/servo,jimberlage/servo,thiagopnts/servo,saneyuki/servo,rnestler/servo,sadmansk/servo,emilio/servo,fiji-flo/servo,fiji-flo/servo,dsandeephegde/servo,avadacatavra/servo,paulrouget/servo,eddyb/servo,CJ8664/servo,avadacatavra/servo,larsbergstrom/servo,paulrouget/servo,saneyuki/servo,larsbergstrom/servo,KiChjang/servo,paulrouget/servo,nnethercote/servo,pyfisch/servo,notriddle/servo,anthgur/servo,larsbergstrom/servo,eddyb/servo,splav/servo,canaltinova/servo,dati91/servo,SimonSapin/servo,dati91/servo,thiagopnts/servo,saneyuki/servo,dsandeephegde/servo,szeged/servo,nnethercote/servo,emilio/servo,thiagopnts/servo,ConnorGBrewster/servo,dati91/servo,canaltinova/servo,SimonSapin/servo,thiagopnts/servo,anthgur/servo,notriddle/servo,larsbergstrom/servo,pyfisch/servo,peterjoel/servo,ConnorGBrewster/servo,KiChjang/servo,notriddle/servo,dsandeephegde/servo,pyfisch/servo,mbrubeck/servo,mbrubeck/servo,upsuper/servo,rnestler/servo,jimberlage/servo,peterjoel/servo,thiagopnts/servo,nnethercote/servo,fiji-flo/servo,dsandeephegde/servo,mbrubeck/servo,jimberlage/servo,CJ8664/servo,ConnorGBrewster/servo,thiagopnts/servo,emilio/servo,emilio/servo,CJ8664/servo,dati91/servo,avadacatavra/servo,notriddle/servo,cbrewster/servo,nnethercote/servo,nnethercote/servo,pyfisch/servo,DominoTree/servo,KiChjang/servo,DominoTree/servo,sadmansk/servo,paulrouget/servo,peterjoel/servo,cbrewster/servo,szeged/servo,sadmansk/servo,szeged/servo,mattnenterprise/servo,pyfisch/servo,szeged/servo,emilio/servo,sadmansk/servo,pyfisch/servo,nnethercote/servo,sadmansk/servo,peterjoel/servo,notriddle/servo,canaltinova/servo,eddyb/servo,upsuper/servo,mattnenterprise/servo,upsuper/servo,splav/servo,jimberlage/servo,splav/servo,cbrewster/servo,saneyuki/servo,ConnorGBrewster/servo,avadacatavra/servo,peterjoel/servo,CJ8664/servo,rnestler/servo,nnethercote/servo,saneyuki/servo,SimonSapin/servo,dati91/servo,eddyb/servo,jimberlage/servo,peterjoel/servo,szeged/servo,mattnenterprise/servo,dsandeephegde/servo,CJ8664/servo,CJ8664/servo,DominoTree/servo,saneyuki/servo,fiji-flo/servo,larsbergstrom/servo,KiChjang/servo,avadacatavra/servo,mattnenterprise/servo,canaltinova/servo,saneyuki/servo