[MacPorts] #58442: gcc9 (and other gccN) fails to install on Mojave, Xcode-10.2.1

[MacPorts]

#58442: gcc9 (and other gccN) fails to install on Mojave, Xcode-10.2.1
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  Reporter:  mouse07410  |      Owner:  (none)
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  gcc9        |
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Comment (by mouse07410):

 > I think your level of expertise, questions, and interest has evolved to
 the point where you can probably dig in helpfully now

 You're flattering me. ;-)

 Two questions. One - is it possible to somehow "virtualize" the
 environment, so that my experiments would be on a cloned/safe copy rather
 than on the main Macports setup? Two - it seems to me that Macports GCC
 should have "-Wa,-q" (or its analog) on by default, because otherwise
 there's no usable assembler anyway. Comments?

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Ticket URL: <https://trac.macports.org/ticket/58442#comment:10>
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