is duplicated by:

• SR-10848 swift 5.1: can't import FoundationNetworking

Issue Description:

Attempting to import FoundationNetworking on Linux with the latest 5.1 snapshot results in:

/home/djones6/swift51/Test/Sources/Test/main.swift:1:8: error: missing required module 'CFURLSessionInterface'
import FoundationNetworking
 ^

This was with 5.1-DEVELOPMENT-SNAPSHOT-2019-05-29-a, which is the latest at the time of writing. I haven't tried other snapshots.

Recreate:

mkdir Test && cd Test && swift package init
echo "import FoundationNetworking" > Sources/Test/Test.swift
swift build