[GHC] #10223: Cleanup `mk/build.mk.sample`

[GHC]

#10223: Cleanup `mk/build.mk.sample`
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        Reporter:  thomie            |                   Owner:  thomie
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by Thomas Miedema <thomasmiedema@…>):

 In [changeset:"2c24fd707f8650205bb574ffac5f376239af3723/ghc"
 2c24fd70/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2c24fd707f8650205bb574ffac5f376239af3723"
 Build system: put each BuildFlavour in a separate file (#10223)

 This allows easier diffing of different BuildFlavours, including
 `mk/flavours/validate.mk`.

 Reviewed By: bgamari, austin

 Differential Revision: https://phabricator.haskell.org/D1050
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10223#comment:8>
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