SI-7695 Macro debug output on -explaintypes

It looks like checkConforms should wait for error before
using explainTypes, rather than turning on macro debug
trace if explaintypes is set.

In particular, macro debug output is Console.println
instead of reporter.echo or similar, so partest can't
test it.
Merge pull request #2772 from som-snytt/issue/6123-fix-test

SI-7695 Macro debug output on -explaintypes