This commit allows ASP.NET Core to be built on arm64 machines directly,
without relying on cross-compilation.
There's a few changes in here:
1. Ask msbuild to look into the BuildArchitecture
By default, our build systems assums the machine is x64. This
modifies the build configuration to check the architecture of the
currently running build machine, and set BuildArchitecture to that.
2. Fix crossgen in Microsoft.AspNetCore.App.Runtime
We run crossgen for supported architectures (including x64 and
arm64). For that, we need a jit that we can point crossgen to.
Generally, we can rely on the build scripts to find the right
`libclrjit.so`. However, arm64 has multiple `libclirjit.so`, for
different use-cases. There's one for arm64 (for running on arm64) and
there's another one for cross-compiling for arm64 on x64. We need to
figure out and use the right one explicitly rather than assuming the
right one gets picked up.
See https://github.com/dotnet/core-setup/pull/8468 for similar
changes made in core-setup.
This also needs https://github.com/aspnet/AspNetCore/pull/14790 to fully
work on arm64.
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