Is it impossible to build ios app(swift) with custom toolchain?

if I build my iPhone12 mini as a target, the error below will occur.
"Unsupported Configuration
The Swift standard library from the toolchain cannot be used on devices.
Select a macOS or simulator run destination instead, or use a diffrent toolchain that only provides the compiler.
Objective C builds well.

The build method is as follows.

brew install cmake ninja
git clone swift
cd swift
utils/update-checkout --tag swift-5.9-RELEASE --clone
utils/build-toolchain MyToolchain

Please let me know if anything is missing.

Offtopic: I'm wondering, even if you succeed, what is the point? There is a topic already about LLVM JIT / LLDB on iOS device Building Swift REPL for iOS . Do you have something else in mind?