Metadata for C++ foreign reference types on Windows isn't emitted

[egorzhdan]

Description

This prevents someone from using foreign reference types on Windows:

swift/lib/IRGen/GenMeta.cpp

Lines 6881 to 6884 in 1ceeb70

	void emitInitializeMetadata(IRGenFunction &IGF, llvm::Value *metadata,
	MetadataDependencyCollector *collector) {
	llvm_unreachable("Not implemented for foreign reference types.");
	}

Reproduction

Try to use a C++ reference-counted type on Windows.

Expected behavior

Code compiles

Environment

Windows

Additional information

No response