Enable library evolution for swift modules

Author: jmschonfeld

CMakeLists.txt

@@ -96,7 +96,8 @@ endif()
 set(_Foundation_swift_build_flags)
 list(APPEND _Foundation_swift_build_flags
     "-DDEPLOYMENT_RUNTIME_SWIFT"
-    "-DSWIFT_CORELIBS_FOUNDATION_HAS_THREADS")
+    "-DSWIFT_CORELIBS_FOUNDATION_HAS_THREADS"
+    "-enable-library-evolution")
 
 if(CMAKE_SYSTEM_NAME STREQUAL "Linux" OR CMAKE_SYSTEM_NAME STREQUAL "Android")
     list(APPEND _Foundation_common_build_flags