Avoid generating module-specific msgid files if project has provided an all-inclusive "cfe_msgids.h" file

[jphickey]

Is your feature request related to a problem? Please describe.
As part of the effort to better compartmentalize the various CFE subcomponents, we are working toward having each module manage its own individual header files.

During this migration, this presents some confusion for a configuration that already has an all-inclusive cfe_msgids.h - as these individual msgid headers will still be generated (with default values) even though they are not used.

Describe the solution you'd like
To reduce confusion -- if the user has a cfe_msgids.h file, then do not generate the individualized msgid files.

Describe alternatives you've considered
The other option would be to revert the focused msgid.h file and go back to having cfe_msgids.h being the only msgid header for CFE.

Additional context
There is a possibility that a user has overridden the cfe_msgids.h but in a way that still #includes some (but perhaps not all) of the focused msgid headers. This proposal would break such a config.... so if that is a real possibility, this might not be a good idea.

Requester Info
Joseph Hickey, Vantage Systems, Inc.

[skliper]

Could just have a cmake flag to turn it off from the user point of view if there's a legitimate use case for users including subcomponent msgid headers from cfe_msgids.h. I can't think of a real need though.... if you want to replace just some, they could just do it at the subcomponent level and use the default cfe_msgids.h.