Fixes System.Runtime.Numerics tests compilation

[marek-safar]

Fixes C# compiler error The out parameter 'num3' must be assigned to before control leaves the current method.

It appears that corefx is using pre-RTM buggy version of C# compiler

[danmoseley]

@mellinoe any interest in getting our compiler updated? :)

[danmoseley]

hang is https://github.com/dotnet/corefx/issues/16602

[danmoseley]

@dotnet-bot test Portable Linux x64 Debug Build please (above)

[mellinoe]

I'm a bit confused. Where are you seeing compilation errors related to this?

[akoeplinger]

@mellinoe we're consuming these tests (from source) in Mono and compiling with Roslyn 2.3 which throws an error because of the wrong C#. The Roslyn 2.0-rc you're using seems to have a bug and compiles this code regardless.

[mellinoe]

Understood! Thanks for the clarification. The code change looks good to me.

[marek-safar]

@danmosemsft @karelz I think it'd make sense to release netcore 2.0 version using RTM version of compiler. We hit this issue only but there can be more hidden problems in code we don't use.

[karelz]

I agree, we should upgrade the compiler. I am surprised we would plan to ship with RC compiler when there is RTM compiler. Filed #20869.