Use the right variable name

Author: Steelskin

cmake/modules/SwiftSupport.cmake

@@ -1,6 +1,6 @@
 include_guard()
 
-if(NOT dispatch_Swift_MODULE_TRIPLE OR NOT dispatch_Swift_ARCH OR NOT dispatch_Swift_SYSTEM)
+if(NOT dispatch_Swift_MODULE_TRIPLE OR NOT dispatch_Swift_ARCH OR NOT dispatch_Swift_PLATFORM)
  # Get the target information from the Swift compiler.
  set(module_triple_command "${CMAKE_Swift_COMPILER}" -print-target-info)
  if(CMAKE_Swift_COMPILER_TARGET)