Micro-optimize guess_library_name()
Micro-optimize guess_library_name()

Per comments on https://github.com/rakudo/rakudo/commit/f6756bb4d9b8b43a55a613a1a2fc85a8c6d379c0#commitcomment-28677139

lucasbuchala/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,Gnouc/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,nbrown/rakudo,MasterDuke17/rakudo,salortiz/rakudo,salortiz/rakudo,labster/rakudo,lucasbuchala/rakudo,tony-o/rakudo,labster/rakudo,salortiz/rakudo,tbrowder/rakudo,softmoth/rakudo,labster/rakudo,tony-o/rakudo,softmoth/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,nbrown/rakudo,rakudo/rakudo,salortiz/rakudo,tony-o/rakudo,nbrown/rakudo,tbrowder/rakudo,rakudo/rakudo,nbrown/rakudo,nbrown/rakudo,labster/rakudo,nbrown/rakudo,MasterDuke17/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,Gnouc/rakudo,rakudo/rakudo,softmoth/rakudo,MasterDuke17/rakudo,tony-o/rakudo,softmoth/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,softmoth/rakudo,labster/rakudo,MasterDuke17/rakudo,tony-o/rakudo,labster/rakudo,salortiz/rakudo,lucasbuchala/rakudo,tony-o/rakudo,rakudo/rakudo,tbrowder/rakudo