testing/dart: replace Wine-based bootstrap with a gcompat one
Currently our Dart package is bootstrapped from a Windows binary ran through Wine. It works but it's of course quite ugly and doomed to fail when Dart changes to use Wine-incompatible instructions.
It is however possible to use a glibc-based build and bootstrap from there, which while not perfect at least gets rid of the Wine dependency in the bootstrapping process. A Dart community member has made Dart builds with tcmalloc disabled which can then be ran through gcompat, which allowed him to build a native Dart build for Musl. We should consider switching our bootstrapping to that; it will also allow us to ship for more architectures.
https://github.com/dart-lang/sdk/issues/40906#issuecomment-1384827698