Variadic FFI test fails on aarch64-apple-darwin

[shepmaster]

x.py test --stage 2 src/test/ui/abi/variadic-ffi

---- [ui] ui/abi/variadic-ffi.rs stdout ----

error: test run failed!
status: exit code: 101
command: "/Users/shepmaster/Projects/rust/full/build/aarch64-apple-darwin/test/ui/abi/variadic-ffi/a"
stdout:
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stderr:
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thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `3078109020`,
 right: `30`', /Users/shepmaster/Projects/rust/src/test/ui/abi/variadic-ffi.rs:78:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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Meta

Fails in e3051d8

[shepmaster]

Based on the porting guide:

Because of these changes, the type va_list is an alias for char*, and not for the struct type in the generic procedure call standard.

So that's one thing that needs to be changed.