Build managed part of crossgen2 as platform independent (AnyCPU)

[gbalykov]

After this change same crossgen2.dll can be launched on different architectures.

Related issue: #31793

cc @alpencolt @jkotas

[jkotas]

Why not build everything as AnyCpu? ie delete https://github.com/dotnet/runtime/blob/master/src/coreclr/dir.common.props#L33

[gbalykov]

@jkotas this change by itself didn't seem to work, and I was not sure whether that was the correct approach, because for example System.Private.CoreLib build relies on Platform set equal to build arch.

[jkotas]

System.Private.CoreLib build relies on Platform set equal to build arch

Set Platform for System.Private.CoreLib, and leave it to default to AnyCPU for everything else?

[jkotas]

None of this should be needed once the default is AnyCPU.

[gbalykov]

@jkotas there is a problem with the approach that sets Platform to AnyCPU for everything.

Crossgen2 is built as an app targeting specific RID (e.g. linux-x64 for x64 build), besides as a self-contained application:

/home/z/Dev/runtime/dotnet.sh publish --self-contained -r linux-x64 -c Release -o /home/z/Dev/runtime/artifacts/bin/coreclr/Linux.x64.Release/crossgen2 /home/z/Dev/runtime/src/coreclr/src/tools/crossgen2/crossgen2/crossgen2.csproj /nologo /p:TargetArchitecture=x64

I've done the change that sets Platform to AnyCPU for everything (gbalykov@703ca05), however, this doesn't affect the resulting dlls, because they still target the specific platform. The same effect is from simple build command instead of publish:

/home/z/Dev/runtime/dotnet.sh build -r linux-x64 -c Release -o /home/z/Dev/runtime/artifacts/bin/coreclr/Linux.x64.Release/crossgen2 /home/z/Dev/runtime/src/coreclr/src/tools/crossgen2/crossgen2/crossgen2.csproj /nologo /p:TargetArchitecture=x64

Only if I remove -r option from there, dlls become platform independent. However, as I understand, crossgen2 is planned to be distributed as a self-contained app, so -r is required: #31741.

On the other side, approach with setting PlatformTarget to AnyCPU works even with build for specific rid. What do you think?

[jkotas]

Hmmm, I have not realized that dotnet publish sets the Platform based on the RID. The change looks good to me as is. Thanks for looking into this.

[jkotas]

Ok, I have not realized we can clean this up later if necessary.