Runtimes: introduce SwiftOnoneSupport

The main goal for now is to have this building, with little
concern about matching the build flags used currently.

Keep it disabled by default on Apple platforms.

Addresses rdar://143151393

Runtimes/Resync.cmake

@@ -78,15 +78,11 @@ set(CoreLibs
   CompatibilityOverride
   stubs
   CommandLineSupport
-  core)
+  core
+  SwiftOnoneSupport)
 
   # Add these as we get them building
-  # core
-  # Concurrency
-  # SwiftOnoneSUpport
-  # CommandLineSupport
   # Demangling
-  # runtime)
 
 foreach(library ${CoreLibs})
   copy_library_sources(${library} "public" "Core")