don't do anything for AWS plugin unless it's enabled

in particular, don't do ExternalProject_Add()
that starts creating build directories for a disabled
plugin

plugin/aws_key_management/CMakeLists.txt

@@ -18,6 +18,12 @@ MACRO(SKIP_AWS_PLUGIN msg)
   RETURN()
 ENDMACRO()
 
+MYSQL_ADD_PLUGIN(aws_key_management aws_key_management_plugin.cc DISABLED
+                 COMPONENT aws-key-management)
+
+IF(NOT TARGET aws_key_management)
+  RETURN()
+ENDIF()
 
 # This plugin needs recent C++ compilers (AWS C++ SDK header files are using C++11 features)
 SET(CXX11_FLAGS)
@@ -145,7 +151,4 @@ ELSE()
 ENDIF()
 
 SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}  ${CXX11_FLAGS}")
-MYSQL_ADD_PLUGIN(aws_key_management aws_key_management_plugin.cc
-                 COMPONENT aws-key-management
-                 LINK_LIBRARIES ${AWS_SDK_LIBS}
-                 DISABLED)
+TARGET_LINK_LIBRARIES(aws_key_management ${AWS_SDK_LIBS})