Consider using S.R.InteropServices.RuntimeInformation.ProcessArchitecture instead pointer based detection of platform

[zabulus]

Follow-up of #381 (comment)

Currently RuntimeInformation.CurrentPlatform is detected based in pointer size: https://github.com/dotnet/BenchmarkDotNet/blob/master/src/BenchmarkDotNet.Core/Portability/RuntimeInformation.cs#L168 and produces wrong result for ARM platform.

Using https://docs.microsoft.com/de-de/dotnet/core/api/system.runtime.interopservices.runtimeinformation#System_Runtime_InteropServices_RuntimeInformation_ProcessArchitecture should fix this issue.

[AndreyAkinshin]

Ok, it easy to do for the CORE profile. Any idea how to detect ARM on Mono?

[zabulus]

Currently on Mono S.R.Interop.RuntimeInformation returns same value as code in BDN:
https://github.com/mono/mono/blob/ff7a2a5114d6da678a5a75c5eebf0731db4f3aed/mcs/class/System.Runtime.InteropServices.RuntimeInformation/System.Runtime.InteropServices/RuntimeInformation.cs#L79

So replacing it won't be regression at least. Though I think this should be fixed in mono

[adamsitnik]

Implemented in #979