Allow build.sh script to be ran from fcs folder
Allow build.sh script to be ran from fcs folder

fixes #851

dsyme/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,Jand42/FSharp.Compiler.Service