fix build portable library
fix build portable library

stratisproject/NStratis,MetacoSA/NBitcoin,MetacoSA/NBitcoin,HermanSchoenfeld/NBitcoin,dangershony/NStratis,you21979/NBitcoin,NicolasDorier/NBitcoin,bitcoinbrisbane/NBitcoin,lontivero/NBitcoin,thepunctuatedhorizon/BrickCoinAlpha.0.0.1