[MacPorts] #55410: gcc7 @7.2.0 does not build on Mac OS X 10.6.8, Snow Leopard, because of "Undefined symbols for architecture x86_64"

[MacPorts]

#55410: gcc7 @7.2.0 does not build on Mac OS X 10.6.8, Snow Leopard, because of
"Undefined symbols for architecture x86_64"
------------------------+-------------------
  Reporter:  ballapete  |      Owner:
      Type:  defect     |     Status:  new
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:  2.4.2
Resolution:             |   Keywords:
      Port:  gcc7       |
------------------------+-------------------

Comment (by kencu):

 tricky. usually the defaults would work, but not in this case as libc++ is
 not the default for clang-3.9 on 10.6.8. So it adds libstdc++, and that
 errors out... kind of a unique situation.

 Would have to strip out the -stdlib flab only if the bootstrap compiler is
 not clang.

 There is another way -- as you may recall, I have altered clang-3.9 on my
 10.6.8 system to default to add -stdlib=libc++ if no -stdlib is present,
 so I would not see this error.

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Ticket URL: <https://trac.macports.org/ticket/55410#comment:4>
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