[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
-------------------------+--------------------
  Reporter:  mouse07410  |      Owner:  (none)
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  gcc9        |
-------------------------+--------------------

Comment (by mouse07410):

 > well it was the default at one point... With the {{{+llvm70}}} variant,
 you get our new {{{as}}} logic... the only real change is which clang will
 get called as the assembler

 It seems that the new {{{as}}}s logic fails, at least on the new systems.
 And the only reliably-working assembler apppears to be the one from native
 Xcode.

 So there has to be a way to either restore {{{+xcode}}} as the default for
 the new systems, or let a user know (maybe in the output of {{{port info
 cctools}}}) - without him having to scour the trac.macports.org searching
 for solution - that the {{{+llvm70}}} default is not going to work.

-- 
Ticket URL: <https://trac.macports.org/ticket/58442#comment:19>
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