This mirrors some existing logic for the bootstrap_target which
influences how TargetPlatform is set.
As described on #21970 not storing this led to `LlvmTarget` being set incorrectly
and hence the wrong `--target` flag being passed to the C compiler.
Towards #21970
This mirrors some existing logic for the bootstrap_target which
influences how TargetPlatform is set.
As described on #21970 not storing this led to `LlvmTarget` being set incorrectly
and hence the wrong `--target` flag being passed to the C compiler.
Towards #21970
