[MacPorts] #51439: ghc: allow building with clang-3.4 or later

[MacPorts]

#51439: ghc: allow building with clang-3.4 or later
--------------------------+----------------------------
  Reporter:  mojca@…      |      Owner:  kitchen.andy@…
      Type:  enhancement  |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  ghc          |
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Comment (by mojca@…):

 Yes, I'm referring to:
 {{{
 port:llvm-3.5
 }}}
 and
 {{{
 set llvmPrefix  ${prefix}/libexec/llvm-3.5
 }}}
 in the `ghc` port.

 If this is also a runtime dependency then variants are probably the only
 way to implement this properly. If it is only a build-time dependency, it
 would be slightly easier. We do something similar to `root6` for example.

 If variants are not desired, it would at least make sense to pick either
 3.4 (probably the lowest supported one; I didn't try 3.3, so I cannot
 tell) or the one that is considered "default" (reasonably high one if not
 the latest one). 3.5 is just weird enough that it causes problems on older
 OSes while not bringing much benefit over 3.4 (3.4 is often the bare
 minimum for C++11, so it is often installed).

-- 
Ticket URL: <https://trac.macports.org/ticket/51439#comment:2>
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