Make the properties of ToolchainConfiguration mutable, allowing easier customization of a single property of an already existing toolchain.  It is already a struct, so the whole struct can be either mutable or immutable based on use.
Make the properties of ToolchainConfiguration mutable, allowing easier customization of a single property of an already existing toolchain.  It is already a struct, so the whole struct can be either mutable or immutable based on use.

abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager