Add NOSYSNUMERICS to netstandard targets.

It seems that serialization support for `Complex` in
`System.Runtime.Numerics` got cleaned up a while ago.  It is
scheduled for reintroduction in `netstandard2.1`.

See the following PR for more info:
https://github.com/dotnet/corefx/pull/20222

src/Numerics/Complex64.cs

@@ -701,7 +701,7 @@ namespace MathNet.Numerics
                 }
             }
 
-#if PORTABLE
+#if PORTABLE || NETSTANDARD
             var value = GlobalizationHelper.ParseDouble(ref token);
 #else
             var value = GlobalizationHelper.ParseDouble(ref token, format.GetCultureInfo());

src/Numerics/Numerics-2017.csproj

@@ -6,7 +6,7 @@
         <PackageId>Math.Numerics</PackageId>
     </PropertyGroup>
     <PropertyGroup Condition="'$(TargetFramework)'=='netstandard1.3'">
-        <DefineConstants>NETSTANDARD</DefineConstants>
+        <DefineConstants>NETSTANDARD;NOSYSNUMERICS</DefineConstants>
     </PropertyGroup>
     <PropertyGroup>
         <OutputPath>..\..\out\test\Net35\</OutputPath>
@@ -22,9 +22,11 @@
         <Reference Include="System.Runtime.Serialization" />
     </ItemGroup>
     <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-        <PackageReference Include="System.Runtime" Version="4.3.0" />
-        <PackageReference Include="System.Runtime.Serialization.Xml" Version="4.3.0" />
-        <PackageReference Include="System.Runtime.Serialization.Formatters" Version="4.3.0" />
-        <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.0" />
+        <PackageReference Include="System.Runtime" Version="4.3.*" />
+        <PackageReference Include="System.Runtime.Numerics" Version="4.3.*" />
+        <PackageReference Include="System.Runtime.Serialization.Xml" Version="4.3.*" />
+        <PackageReference Include="System.Runtime.Serialization.Primitives" Version="4.3.*" />
+        <PackageReference Include="System.Runtime.Serialization.Formatters" Version="4.3.*" />
+        <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.*" />
     </ItemGroup>
 </Project>

src/UnitTests/UnitTests-2017.csproj

@@ -8,8 +8,8 @@
         <AssemblyName>MathNet.Numerics.UnitTests</AssemblyName>
         <RootNamespace>MathNet.Numerics.UnitTests</RootNamespace>
     </PropertyGroup>
-    <PropertyGroup Condition="$(TargetFramework.Contains('netcoreapp'))">
-        <DefineConstants>NETSTANDARD</DefineConstants>
+    <PropertyGroup Condition="$(TargetFramework.Contains('netcoreapp')) OR $(TargetFramework.Contains('netstandard'))">
+        <DefineConstants>NETSTANDARD;NOSYSNUMERICS</DefineConstants>
     </PropertyGroup>
     <ItemGroup Condition="'$(TargetFramework)' == 'net45'">
         <Reference Include="System" />
@@ -19,7 +19,7 @@
         <Reference Include="System.Runtime.Serialization" />
         <Reference Include="System.Xml" />
     </ItemGroup>
-    <ItemGroup Condition="$(TargetFramework.Contains('netcoreapp'))">
+    <ItemGroup Condition="$(TargetFramework.Contains('netcoreapp')) OR $(TargetFramework.Contains('netstandard'))">
         <PackageReference Include="System.Reflection" Version="4.3.*" />
         <PackageReference Include="System.Reflection.Extensions" Version="4.3.*" />
         <PackageReference Include="System.Reflection.TypeExtensions" Version="4.4.*" />
@@ -33,7 +33,7 @@
       <ProjectReference Include="..\Numerics\Numerics-2017.csproj" />
       <ProjectReference Include="..\TestData\TestData-2017.csproj" />
     </ItemGroup>
-    <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp1.1' ">
+    <ItemGroup Condition="$(TargetFramework.Contains('netcoreapp')) OR $(TargetFramework.Contains('netstandard'))">
         <PackageReference Include="System.Xml.XmlSerializer" Version="4.3.*" />
     </ItemGroup>
 </Project>