In practice, thanks to all the registers the stubs don't actually change,
but it's confusing to have an incorrect declaration.
I suspect that fcntl remains broken for aarch64; it happens to work for
x86_64 because the first vararg argument gets placed in the right register
anyway, but I have no reason to believe that's true for aarch64.
This patch adds a unit test, though, so we'll be able to tell when we get
as far as running the unit tests.
Change-Id: I58dd0054fe99d7d51d04c22781d8965dff1afbf3
