[SR-8670] Make SwiftSyntax available on Linux

[akyrtzi]

Previous ID	SR-8670
Radar	None
Original Reporter	@akyrtzi
Type	Task
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	SwiftSyntax
Labels	Task
Assignee	@spevans
Priority	Medium

md5: e7e04b596cc8904fe80c0bfdf1f911b3

Issue Description:

SwiftSyntax is currently only supported on Darwin, we should make the necessary changes to make it available for linux as well. For example SwiftSyntax depends on Foundation, for the linux build it can depend on swift-corelibs-foundation.

[spevans]

#5 fixes the I/O reading from the swiftc subprocess and also fixes the tests to work correctly.