exporting a C var args function triggers LLVM assertion when targeting non-Darwin aarch64

[andrewrk]

Zig Version

0.11.0-dev.986+5ca1753ff

Steps to Reproduce and Observed Behavior

Enable the disabled behavior tests and then:

$ stage3/bin/zig test ../test/behavior.zig -I../test -target aarch64-windows
LLVM Emit Object... zig: /home/andy/Downloads/llvm-project-15/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:8597: llvm::SDValue llvm::AArch64TargetLowering::LowerVAARG(llvm::SDValue, llvm::SelectionDAG&) const: Assertion `Subtarget->isTargetDarwin() && "automatic va_arg instruction only works on Darwin"' failed.

Expected Behavior

tests passed