Sylvain Henry authored Jan 07, 2021 and Marge Bot committed Feb 13, 2021

Before this patch, the only way to override GHC's default logging
behavior was to set `log_action`, `dump_action` and `trace_action`
fields in DynFlags. This patch introduces a new Logger abstraction and
stores it in HscEnv instead.

This is part of #17957 (avoid storing state in DynFlags). DynFlags are
duplicated and updated per-module (because of OPTIONS_GHC pragma), so
we shouldn't store global state in them.

This patch also fixes a race in parallel "--make" mode which updated
the `generatedDumps` IORef concurrently.

Bump haddock submodule

The increase in MultilayerModules is tracked in #19293.

Metric Increase:
    MultiLayerModules