The _Builtin_float symbols were moved twice, most recently from the OS Darwin library, but previously they were in the embedded @rpath Darwin library. @_originallyDefinedIn doesn't support multiple install names, but it can be replaced with -module-abi-name, and then multiple $ld$previous$ symbols can be used.
Update the Platform and Concurrency magic symbols to use $ld$previous$ everywhere.
rdar://130107191
