cmake: better auto *.i targets in Makefiles

cmake/maintainer.cmake

@@ -56,3 +56,10 @@ ELSEIF(MYSQL_MAINTAINER_MODE MATCHES "AUTO")
   SET(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} ${MY_MAINTAINER_C_WARNINGS}")
   SET(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${MY_MAINTAINER_CXX_WARNINGS}")
 ENDIF()
+
+IF(CMAKE_C_COMPILER_ID MATCHES "GNU")
+  STRING(REPLACE " -E " " -E -dDI " CMAKE_C_CREATE_PREPROCESSED_SOURCE ${CMAKE_C_CREATE_PREPROCESSED_SOURCE})
+ENDIF()
+IF(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+  STRING(REPLACE " -E " " -E -dDI " CMAKE_CXX_CREATE_PREPROCESSED_SOURCE ${CMAKE_CXX_CREATE_PREPROCESSED_SOURCE})
+ENDIF()