Merge pull request #35358 from DougGregor/concurrency-without-darwin

[Concurrency] Drop dependency on the Darwin overlay

Author: DougGregor

stdlib/public/Concurrency/CMakeLists.txt

@@ -50,10 +50,6 @@ add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   Mutex.cpp
   ${swift_concurrency_objc_sources}
 
-  SWIFT_MODULE_DEPENDS_OSX Darwin
-  SWIFT_MODULE_DEPENDS_IOS Darwin
-  SWIFT_MODULE_DEPENDS_TVOS Darwin
-  SWIFT_MODULE_DEPENDS_WATCHOS Darwin
   SWIFT_MODULE_DEPENDS_LINUX Glibc
   SWIFT_MODULE_DEPENDS_FREEBSD Glibc
   SWIFT_MODULE_DEPENDS_OPENBSD Glibc