[GHC] #10536: Clear up how to turn off dynamic linking in build.mk

[GHC]

#10536: Clear up how to turn off dynamic linking in build.mk
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        Reporter:  thomie            |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Build System      |                 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:"37de4ad76b75d403e6a8dae9539af08c859d46a4/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="37de4ad76b75d403e6a8dae9539af08c859d46a4"
 Build system: don't set GhcLibWays explicitly in build.mk.sample (#10536)

 We used to have the following in mk/build.mk.sample:

   GhcLibWays = $(if $(filter $(DYNAMIC_GHC_PROGRAMS),YES),v dyn,v)

 This commit removes that statement for the following reasons:

   1) It depends on the variable DYNAMIC_GHC_PROGRAMS, which is set later
      in the file for some BuildFlavours. Although this works because
      `make` does multiple passes when reading Makefiles, it is confusing
      to users [1]. Instead, test for DYNAMIC_GHC_PROGRAMS in
      mk/config.mk.in.

   2) Although it looks like that line is about compiling the `dyn` way,
      its purpose is really to not build the `prof` way. This commit
      introduces the variable BUILD_PROF_LIBS, to make this more
      explicit.

 This simplifies mk/build.mk.sample and mk/validate-settings.mk.

 Note that setting GhcLibWays explicitly still works, and
 DYNAMIC_GHC_PROGRAMS=NO in build.mk does not build the `dyn` way.

 [1] https://mail.haskell.org/pipermail/ghc-devs/2014-December/007725.html

 Differential Revision: https://phabricator.haskell.org/D1021
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10536#comment:1>
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