[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 ryandesign):

 Replying to [comment:3 ryandesign]:
 > The compile line you showed that invokes `clang++-mp-3.9` clearly
 doesn't contain `-stdlib=libc++`, which is why it failed.

 At least I assumed that was why it failed. But that would only make sense
 if it was trying to link with a dependency's library which used C++, and I
 can't see any of gcc's dependencies that use C++. So maybe it's failing
 for a different reason. Please try gcc7 @7.3.0 and if it still fails
 please attach a new log.

 Replying to [comment:4 kencu]:
 > Would have to strip out the -stdlib flab only if the bootstrap compiler
 is not clang.

 MacPorts base only adds `-stdlib` in the first place if the compiler is
 clang. See `proc portconfigure::should_add_stdlib` in [browser:macports-
 base/src/port1.0/portconfigure.tcl].

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Ticket URL: <https://trac.macports.org/ticket/55410#comment:5>
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