pod_support_buildable not present when not vendored

I get the following error when trying to build RCT-Folly. It seems that this is an internal detail of PodToBUILD, and the expected file has not been generated. I plan to try vendored mode to see if I encounter the same issue.

```
no such package '@RCT-Folly//pod_support_buildable': BUILD file not found in directory 'pod_support_buildable' of external repository @RCT-Folly. Add a BUILD file to a directory to mark it as a package. and referenced by '@RCT-Folly//:Fabric_acknowledgement'
```