[MacPorts] #54129: llvm-4.0 build fails due to libtool error on SnowLeopard when built with clang-3.9, but succeeds when built with clang-3.7

[MacPorts]

#54129: llvm-4.0 build fails due to libtool error on SnowLeopard when built with
clang-3.9, but succeeds when built with clang-3.7
-----------------------+----------------------
  Reporter:  kencu     |      Owner:  jeremyhu
      Type:  defect    |     Status:  accepted
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  llvm-4.0  |
-----------------------+----------------------

Comment (by Ionic):

 No, it doesn't. `${configure.compiler}` is being used before blacklisting,
 which keeps it at `gcc-4.2` and hence any dependencies upon `cctools` are
 not added to `depends_build`. This holds for unpatched base.

 The situation is different if I backport your base patch (though we cannot
 rely on that for the moment): since the `cctools` dependency is added by
 base early enough, the `cmake` option is also added in the `pre-configure`
 block.

 Take a look at these two log files - one made with vanilla base, the other
 one with the backported patch.

 For now, we should delay both blocks by putting them into the `pre-
 configure` phase.

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Ticket URL: <https://trac.macports.org/ticket/54129#comment:26>
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