Introducing PR verification x86 CI build

[artidoro]

Fixes #1389.

This PR adds a PR verification build for x86. Starting an x86 build is not too difficult, however running tests requires downloading an x86 .NET Core SDK

Main contributions:

• runs debug and release x86 build
• depending on the argument -buildArch=x86 it will download the .NET Core SDK for x86 or for x64 to be able to run the tests

[Ivanidzo4ka]

We need to put conditions on TensorFlow transform tests since it's work only with x64 bits (at least from what I see from test failure).
Here is example:

machinelearning/test/Microsoft.ML.OnnxTransformTest/OnnxTransformTests.cs

Line 60 in a285f8d

[ConditionalFact(typeof(Environment), nameof(Environment.Is64BitProcess))] // x86 fails with "An attempt was made to load a program with an incorrect format."

#Resolved

[eerhardt]

Looks good so far. Just need to get the tests passing.

[danmoseley]

Seems that int precision = digitsOfPrecision ?? (Environment.Is64BitProcess ? DigitsOfPrecision_x64 : DigitsOfPrecision_x86); could be pulled out into a property like public int DigitsOfPrecision => Environment.Is64BitProcess ? DigitsOfPrecision_x64 : DigitsOfPrecision_x86; rather than repeated #Resolved

[artidoro]

I found that having a different precision was not helpful, so I reverted that change. Thank you for the comment though!

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In reply to: 227575101 [](ancestors = 227575101)

[tannergooding]

LGTM

[adamsitnik]

@artidoro regarding the failing benchmark integration test. You can add the [ConditionalFact(typeof(Environment), nameof(Environment.Is64BitProcess))] for it as well and create a new issue to fix it and assign me. #Resolved

[eerhardt]