[vcpkg script] Add Clang as ObjC Compiler when generating meson build

[Naville]

Describe the pull request

• What does your PR fix?

WIP. Don't merge Fixes #26147

• Which triplets are supported/not supported? Have you updated the CI baseline?

NO

• Does your PR follow the maintainer guide?

Probably? This is more of an PoC rather than an actual PR

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

NO

• Rationale

Clang is the only "officially" supported ObjC Compiler by Apple, so I think it's ok to enforce Clang here.
Although, we might want to add missing checks when Clang doesnt exist, or similar QoL improvements to this quick and dirty patch