[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:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by thomie):

 Phab:D783 filters out `-Rghc-timing` for `V=0` builds.

 I didn't make any changes to the default `V=1` build, as `-Rghc-timing`
 has been part of that default since at least the beginning of the century,
 some  people might depend on it, and it could be useful for bug reports.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10223#comment:2>
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