Enable x86 performance runs

[lt72]

[rynowak]

We'd like to do this with dotnet cache https://github.com/dotnet/core-proposals/blob/master/DotNetCore-SharedPackageStore.md We don't want to script more complex logic for running crossgen if we can avoid it.

[rynowak]

@lt72 - this is unblocked now

[rynowak]

assigned to @davmason

[rynowak]

@davmason done?

[davmason]

Not done yet