Fix read-after-write dependencies in pool_block_remove (#2207)
Fix read-after-write dependencies in pool_block_remove (#2207)

This change allows compiler optimisations to be less conservative. This
doesn't include any functional change.
cquinn/ponyc,boemmels/ponyc,jemc/ponyc,sgebbie/ponyc,Praetonus/ponyc,kulibali/ponyc,Theodus/ponyc,kulibali/ponyc,cquinn/ponyc,Perelandric/ponyc,jemc/ponyc,ponylang/ponyc,dipinhora/ponyc,Theodus/ponyc,boemmels/ponyc,sgebbie/ponyc,boemmels/ponyc,Perelandric/ponyc,sgebbie/ponyc,boemmels/ponyc,ponylang/ponyc,kulibali/ponyc,cquinn/ponyc,CausalityLtd/ponyc,dipinhora/ponyc,cquinn/ponyc,Perelandric/ponyc,dipinhora/ponyc,Praetonus/ponyc,Praetonus/ponyc,Perelandric/ponyc,jemc/ponyc,boemmels/ponyc,sgebbie/ponyc,Theodus/ponyc,kulibali/ponyc,ponylang/ponyc,Theodus/ponyc,Praetonus/ponyc,Theodus/ponyc,Perelandric/ponyc,CausalityLtd/ponyc,CausalityLtd/ponyc,sgebbie/ponyc