debug output

[Simon Peyton Jones]

mk/flavours/validate.mk has

GhcStage2HcOpts    = -O -dcore-lint

GhcLibHcOpts       = -O -dcore-lint
How can I override these in my validate.mk?  E.g.

GhcLibHcOpts      += -ddebug-output
does not work.
Thanks. One should really be able to override anything.
Simon

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