Add support for passing additional arguments to IBTool/ACTool

There's a new interface builder compilation mode in Xcode 27, which can be opted out of:

"Introducing a new Interface Builder compilation mode, toolchain, for UIKit (Cocoa Touch) based documents. Enabled by default, toolchain allows compiling IB documents without the need to download a simulator, which is especially useful for build servers. Should you experience issues during this transition period, you can opt out via the IBC_COCOATOUCH_COMPILER_MODE = simulator build setting or using --cocoatouch-compiler-mode simulator when manually invoking ibtool. If you opt out, please file Feedback and include any errors you may have received from ibtool so we can investigate."

Adding support for additional arguments to IBTool/ACTool would make it possible for customers to opt out.