[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
-------------------------------------+-------------------------------------
        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:  Phab:D1021
-------------------------------------+-------------------------------------

Comment (by int-e):

 Could we still mention `GhcLibWays` in `build.mk.sample`? For example,
 under `Other settings...`:

 {{{
 # Set library ways directly instead of computing it from BUILD_PROF_LIBS
 and
 # DYNAMIC_GHC_PROGRAMS (may result in build failures)
 #GhcLibWays = v dyn p
 }}}

 On the topic of `DYNAMIC_GHC_PROGRAMS`, I believe the logic for enabling
 the `dyn` way is as follows: Since the flag implies that ghci is linked
 dynamically, using the dynamic rts, that means ghci requires the `dyn`
 libraries in order to work.

 Also regarding the semantics, `DYNAMIC_BY_DEFAULT` is another option which
 affects the usability of the resulting ghc: on Linux (presumably the story
 on Windows is different) Cabal doesn't interact with the resulting ghc
 properly if the vanilla way is enabled in Cabal's configuration, resulting
 in obscure build failures.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10536#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler