Merge branch 'ibmi-aix-exports' into release-3.16

Merge-request: !4611

Source/cmTarget.cxx

@@ -235,8 +235,11 @@ cmTarget::cmTarget(std::string const& name, cmStateEnums::TargetType type,
     !impl->Makefile->GetSafeDefinition("CMAKE_IMPORT_LIBRARY_SUFFIX").empty();
 
   // Check whether we are targeting AIX.
-  impl->IsAIX =
-    (impl->Makefile->GetSafeDefinition("CMAKE_SYSTEM_NAME") == "AIX");
+  {
+    std::string const& systemName =
+      impl->Makefile->GetSafeDefinition("CMAKE_SYSTEM_NAME");
+    impl->IsAIX = (systemName == "AIX" || systemName == "OS400");
+  }
 
   // Check whether we are targeting an Android platform.
   impl->IsAndroid =