Allow caffe2 to build with fbcode/mode/mac (#87293)
Summary: The Mac contbuild builds under the `fbcode/mode/mac` which caffe2 fails to build under. This is due to that build mode enforcing protobuf v3. The caffe2 targets already account for this issue under `arvr` build modes by swapping out protobuf dependencies. They don't account for the same issue under `fbcode/mode/mac`. This diff fixes that by checking for `is_fbcode_mac` in these situations (in addition to `arvr`).
Test Plan:
```
buck build --flagfile fbsource//fbcode/mode/mac fbsource//xplat/caffe2/...
```
Reviewed By: kimishpatel
Differential Revision: D39552724
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87293
Approved by: https://github.com/kimishpatel
