[MacPorts] #41154: openscad: fix build with libc++

[MacPorts]

#41154: openscad: fix build with libc++
------------------------+-------------------------------
  Reporter:  ecronin@…  |      Owner:  macsforever2000@…
      Type:  defect     |     Status:  new
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:  2.2.1
Resolution:             |   Keywords:  mavericks libc++
      Port:  openscad   |
------------------------+-------------------------------

Comment (by ecronin@…):

 {{{src/stl-utils.cc}}} has a bad #if, it's what needs patching not the
 portfile (other than to include the new patchfile in the Portfile).

 For ports' purposes, just include the ciso646 header and make
 {{{defined(__APPLE__) && defined(__GNUC__)}}} be {{{defined(__APPLE__) &&
 defined(__GNUC__) && !defined(_LIBCPP_VERSION)}}} so that with libc++ the
 file becomes a big noop.  That should be able to be applied safely
 regardless of the compiler/os/stdlib used by macports.  Upstream might
 want to fix it better by explicitly checking for the broken version(s) of
 gcc or libstdc++ instead of adding on all the things that aren't broken,
 although a 3rd stdlib for {{{__APPLE__}}} seems unlikely...

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Ticket URL: <https://trac.macports.org/ticket/41154#comment:3>
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