Fix root cause of duplicated SDK targets

Drop deduplication of such lists so to surface configuration errors
earlier.

Author: edymtt

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -1689,7 +1689,6 @@ function(add_swift_target_library name)
     set(SWIFTLIB_TARGET_SDKS ${SWIFT_SDKS})
   endif()
   list_replace(SWIFTLIB_TARGET_SDKS ALL_APPLE_PLATFORMS "${SWIFT_DARWIN_PLATFORMS}")
-  list(REMOVE_DUPLICATES SWIFTLIB_TARGET_SDKS)
 
   # All Swift code depends on the standard library, except for the standard
   # library itself.

stdlib/public/Platform/CMakeLists.txt

@@ -17,7 +17,7 @@ if(SWIFT_ENABLE_REFLECTION)
 endif()
 
 set(swiftDarwin_target_sdks ALL_APPLE_PLATFORMS)
-if(SWIFT_FREESTANDING_FLAVOR STREQUAL "apple")
+if(SWIFT_FREESTANDING_FLAVOR STREQUAL "apple" AND NOT SWIFT_FREESTANDING_IS_DARWIN)
   set(swiftDarwin_target_sdks ALL_APPLE_PLATFORMS FREESTANDING)
 endif()