Bounty for -minimal compiler flag

[Kagamin]

I don't think, everything should be done by the compiler. Most 
trouble with gc is that its usage can't be traced similar to tls, 
so the feature will be diagnostics similar to -vtls option, say, 
-vminimal. The compiler can write the trace of runtime usage in 
machine-readable format to stdout (format: 
`vminimal:feature:file:line`) and a separate frontend (stylesop) 
can analyze the trace and apply arbitrary feature usage policy. 
Don't change semantics of language constructs. The first step 
would be to implement tracing of gc usage.