Support linking against tbd-v3 SDKs such as those bundled with
Xcode 10.3 → 11.3.1 .

- Map target os=`ios` and abi=`macabi` to macho.PLATFORM.MACCATALYST.
  This allows for matches against tbdv4 targets, eg. `x86_64-maccatalyst`.

- When parsing old tbdv3 files with `zippered` platform, we append
  [`ARCH-macos`, `ARCH-maccatalyst`] to list of "tbd" targets. This
  enables linking for standard targets like `ARCH-macos-none` and
  maccatalyst targets `ARCH-ios-macabi`.

- Update mappings for macho platform and zig target macabi. While this
  is not full maccatalyst support, a basic exe can be built as follows:

```
zig libc > libc.txt
zig build-exe z0.zig --libc libc.txt -target x86_64-ios-macabi
```

closes #19110