[foreign-memaccess+abi] RFR: 8287516: Implement fallback Linker [v6]

Fri Jan 20 16:00:30 UTC 2023

On Fri, 20 Jan 2023 15:45:05 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> We can never encounter a union layout in this code. In libffi they are represented as a single element struct.
>
> Support for unions is not implemented in the fallback linker at the moment [1](https://github.com/openjdk/panama-foreign/pull/770/files#diff-b2d5d47f7117501ef2f8d7c497f0e2d999ac4374ae0a17aacaf12590cb2fc111R116). I wanted to do that as part of: https://bugs.openjdk.org/browse/JDK-8300294 when we have some tests, and there might be issues on other linkers as well that need fixing.

I've changed the parameter type to `StructLayout` to make this more clear.

-------------

PR: https://git.openjdk.org/panama-foreign/pull/770