Stop making src modifications to every repo's eng/common/tools.sh

[MichaelSimons]

When building the VMR, there are several checked in files that are being modified. This yields a poor UX as these must be undone before you can build cleanly again. These edits will also become a nuisance in .NET 9 when the VMR can be used to checkin changes.

One type of file being modified is each repo's repo's eng/common/tools.sh. This file is updated to workaround #2307

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[NikolaMilosavljevic]

@MichaelSimons @mmitche - source-build is modifying eng/common/tools.sh to update the following line: https://github.com/dotnet/arcade/blob/f5d1610c0943aefc60193d26c43736b2c61a8ed6/eng/common/tools.sh#L512 to return $exit_code instead of 0.

The following 2 environment variables are available during Bash script execution, and can be used to push the VMR change upstream, which would add some source-build conditioned code:

DotNetBuildFromSource=true
DotNetBuildFromSourceFlavor=Product

The alternative would be to dig deeper and understand if we could either: 1) drop source-build change altogether, or 2) modify Arcade's code to return $exit_code. Option 2 would run against the following comment and likely introduce extra logging noise - it's unknown if noise is all that would be added, or if some CI log-parsing code would fail. Here's the existing comment in Arcade: https://github.com/dotnet/arcade/blob/f5d1610c0943aefc60193d26c43736b2c61a8ed6/eng/common/tools.sh#L509-L512

[mmitche]

Does the history indicate why source-build changed to update this to return $exit_code?