[Downstream Change] Extend the Multilib system to support an IncludeDirs field #446
Description
What is the change
This patch extends the Multilib Yaml format to allow specifying an IncludeDirs for the header path/s per multilib variant. The goal is to enable fine-grained control over header search paths for each multilib variant. This feature is especially useful in setups where header paths deviate from the default bare-metal assumptions. For example, when headers are shared across target triples, it becomes necessary to organise them under target-triple-specific directories to ensure correct resolution.
Why this change cannot be done upstream
This is already in upstream review llvm/llvm-project#146651. Since the review is pending, a downstream patch is made to enable IncludeDirs support in multilib.yaml