true 实现通用的实用功能。 netstandard2.0;netcoreapp3.1;net461;net40;net20 NETSTD;HAVE_ASYNC;HAVE_BIG_INTEGER;$(DefineConstants);$(AdditionalConstants) NETSTD;HAVE_ASYNC;HAVE_BIG_INTEGER;$(DefineConstants);$(AdditionalConstants) NETFX;NET20;DRAWING;$(DefineConstants);$(AdditionalConstants) NETFX;NET40;DRAWING;HAVE_BIG_INTEGER;$(DefineConstants);$(AdditionalConstants) NETFX;NET461;NET45;DRAWING;HAVE_ASYNC;HAVE_BIG_INTEGER;$(DefineConstants);$(AdditionalConstants) HAVE_ASYNC;HAVE_BIG_INTEGER;$(DefineConstants);$(AdditionalConstants)