Emit vtables/type infos with weak ODR linkage for MachO compatibility

[marcauberer]

Problem

Since the bootstrap accept()-dispatch commits, macOS CI fails to link BootstrapCompilerTests.bootstrapCompiler_unitWrapperAstVisualizer:

duplicate symbol 'vtable for IAbstractAstVisitor' in:
    .../abstract-ast-visitor-intf.o
    .../abstract-ast-visitor.o
ld: 3 duplicate symbols

IAbstractAstVisitor is deliberately declared in two files — an empty forward declaration in abstract-ast-visitor-intf.spice (so ast-nodes.spice can type accept(IAbstractAstVisitor*) without a circular import) and the full typed interface in abstract-ast-visitor.spice. Both translation units emit the vtable/typeinfo/typeinfo name symbols.

These were emitted as strong ExternalLinkage symbols relying on a comdat group to coalesce the duplicates. attachComdatToSymbol skips comdat on MachO (macOS has no comdat support), so on macOS the two strong definitions collide. On ELF the comdat coalesces them, which is why Linux CI was green.

Fix

VTables, type infos and type info names are ODR entities that can legitimately appear in multiple translation units. Emit them with WeakODRLinkage instead of strong external, exactly as Clang emits C++ vtables/type infos:

• ELF: pairs with the existing comdat group — behavior unchanged, still coalesced.
• MachO: the weak/coalesced linkage lets the linker merge the duplicates instead of erroring.

Regular functions and global variables are unaffected (they still use getSymbolLinkageType).

Tests

• The previously-failing bootstrapCompiler_unitWrapperAstVisualizer and the interface/bootstrap-linker tests pass (22/22).
• Full IRGeneratorTests suite passes (171/171).
• Only two reference IR files changed (success-cross-sourcefile-interfaces), regenerated via --update-refs; the only delta is the weak_odr prefix on the public vtable/type info, matching standard Clang codegen.

🤖 Generated with Claude Code

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