[GHC] #11429: Make unrecognised `-W` flags a warning rather than an error

[GHC]

#11429: Make unrecognised `-W` flags a warning rather than an error
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                Owner:  bgamari
            Type:  feature request   |               Status:  patch
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1830
       Wiki Page:  Design/Warnings   |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"f0f63b39783055b2c0c1a8db8c22749afa6d7329/ghc"
 f0f63b39/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f0f63b39783055b2c0c1a8db8c22749afa6d7329"
 Implement -Wunrecognised-warning-flag

 This allows the user to avoid warnings for warning flags that GHC
 doesn't recognise. See #11429 for details..

 Test Plan: Validate with T11429[abc] tests

 Reviewers: austin, hvr

 Reviewed By: hvr

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1830

 GHC Trac Issues: #11429
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11429#comment:5>
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