[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 Thomas Miedema <thomasmiedema@…>):

 In [changeset:"4c1e1c870e294990a44d8d6837742fb0d00f5456/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4c1e1c870e294990a44d8d6837742fb0d00f5456"
 Disable same warnings for normal builds as for validate (#10223)

 The default validate settings currently disable some warnings in the
 libraries. This patch moves those settings to a new file called
 `mk/warnings.mk`, and applies them also to normal builds.

 Through uncommenting a line in build.mk, developers can now build with
 -Werror.

 -Werror is not the default, because:
 * We can not guarantee that the build is warning free on platforms we
   don't run regularly run validate (as part of continuous integration
   systems), and we still want the build to go through on those
   platforms.
 * quoting rwbarton on irc > "I think -Werror by default has come up in
   the past and the argument was that it is too annoying when you are
   doing nontrivial development"

 Reviewed By: austin

 Differential Revision: https://phabricator.haskell.org/D785
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10223#comment:6>
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