Use more target centric code

src/kmailtransport/plugins/smtp/CMakeLists.txt

 if (BUILD_TESTING)
     add_subdirectory(autotests)
 endif()
+kcoreaddons_add_plugin(mailtransport_smtpplugin JSON smtpmailtransport.json INSTALL_NAMESPACE mailtransport)
 
-set(mailtransport_smtpplugin_SRCS
+target_sources(mailtransport_smtpplugin PRIVATE
     smtpmailtransportplugin.cpp
     smtpconfigdialog.cpp
     smtpjob.cpp
     smtpconfigwidget.cpp
     )
-ki18n_wrap_ui(mailtransport_smtpplugin_SRCS
+ki18n_wrap_ui(mailtransport_smtpplugin
     smtpsettings.ui
     )
-ecm_qt_declare_logging_category(mailtransport_smtpplugin_SRCS HEADER mailtransportplugin_smtp_debug.h IDENTIFIER MAILTRANSPORT_SMTP_LOG CATEGORY_NAME org.kde.pim.mailtransport.smtpplugin
+ecm_qt_declare_logging_category(mailtransport_smtpplugin HEADER mailtransportplugin_smtp_debug.h IDENTIFIER MAILTRANSPORT_SMTP_LOG CATEGORY_NAME org.kde.pim.mailtransport.smtpplugin
         DESCRIPTION "kmailtransport (smtp plugin)"
         OLD_CATEGORY_NAMES log_smtp
         EXPORT MAILTRANSPORT
     )
 
 
-kcoreaddons_add_plugin(mailtransport_smtpplugin JSON smtpmailtransport.json SOURCES
-    ${mailtransport_smtpplugin_SRCS} INSTALL_NAMESPACE mailtransport)
 
 target_link_libraries(mailtransport_smtpplugin
     KF5::MailTransport

src/kmailtransportakonadi/plugins/CMakeLists.txt

-set(mailtransport_akonadiplugin_SRCS
+kcoreaddons_add_plugin(mailtransport_akonadiplugin JSON akonadimailtransport.json INSTALL_NAMESPACE mailtransport)
+target_sources(mailtransport_akonadiplugin PRIVATE
     akonadimailtransportplugin.cpp
     resourcesendjob.cpp
     )
 
-ecm_qt_declare_logging_category(mailtransport_akonadiplugin_SRCS HEADER mailtransportplugin_akonadi_debug.h IDENTIFIER
+ecm_qt_declare_logging_category(mailtransport_akonadiplugin HEADER mailtransportplugin_akonadi_debug.h IDENTIFIER
         MAILTRANSPORT_AKONADI_LOG CATEGORY_NAME org.kde.pim.mailtransport.akonadiplugin
         DESCRIPTION "kmailtransport (akonadi plugin)"
         EXPORT MAILTRANSPORT
@@ -11,8 +12,6 @@ ecm_qt_declare_logging_category(mailtransport_akonadiplugin_SRCS HEADER mailtran
 
 
 
-kcoreaddons_add_plugin(mailtransport_akonadiplugin JSON akonadimailtransport.json SOURCES
-    ${mailtransport_akonadiplugin_SRCS} INSTALL_NAMESPACE mailtransport)
 
 target_link_libraries(mailtransport_akonadiplugin
     KF5::MailTransportAkonadi