Provide a way to not pass -DCMAKE_EXPORT_COMPILE_COMMANDS=ON in the cmake invocation

[anarthal]

At the moment, mrdocs appends a -DCMAKE_EXPORT_COMPILE_COMMANDS=ON at the end of the command line. This might be too much for some projects, as it generates the compilation database for all targets in the project (as per the cmake docs).

I can't disable some of the targets built by my project, because they're added by dependencies. In this case, I'd like to set the EXPORT_COMPILE_COMMANDS manually for the target I'd like MrDocs to know about. This would allow me to generate a compile_commands.json that has only the targets relevant to MrDocs, without modifying my dependencies.

[anarthal]

As noted by Peter, this can be solved by passing mrdocs options before user options, so they can be overriden. This would fix my issue.

[alandefreitas]

Also noted by peter, instead of an option, we could simply not change if it's there -DCMAKE_EXPORT_COMPILE_COMMANDS=OFF.