[Parse] Add suggestion to targetEnvironment diagnostic.

Author: graydon

include/swift/AST/DiagnosticsParse.def

@@ -1504,7 +1504,8 @@ WARNING(unknown_platform_condition_argument,none,
       "unknown %0 for build configuration '%1'",
       (StringRef, StringRef))
 WARNING(likely_simulator_platform_condition,none,
-      "plaform condition appears to be testing for simulator environment",
+      "plaform condition appears to be testing for simulator environment; "
+      "use 'targetEnvironment(simulator)' instead",
       ())
 
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