avoid "use ExtUtils::MakeMaker 0;"
build the prereqs attr lazily
slightly quieten main_module logic so only guessed modules log

That is, if a user sets main_module explicitly, it doesn't log without
-v.

Auto-guessing still logs, and we could disable that too, but this is a
minimal fix so people who want to explicitly repress that log can do so.
downgrade 'extracting distribution abstract' notice to debug

The frequency of this being important context is low.
add changelog entries