The current target's ABI cannot be relied on for this.
For example, we may build the zig compiler for target
riscv64-linux-musl and provide a tarball for users to
download. A user could then run that zig compiler on
riscv64-linux-gnu. This use case is well-defined and
supported by Zig. But that means that we must detect
the system ABI here rather than
relying on `std.Target.current`.