[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        |
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Comment (by cjones051073):

 Just found my may to this ticket.... A few comments.

 The cctools Xcode variant indeed was the default, for a while, as it was
 done to fix issues with the as from cctools being very very old and unable
 to handle the output from modern compilers.

 Then, the maintainer updated the port, and made the llvm variants the
 default again, for reasons he did not care to share. Also note the
 maintainer works for Apple, and as such is not going to be any help with
 gcc as he cannot even look at code that is GPL3...

 So then, later on, the logic currently in cctools was added to enhance the
 way it checks for the 'system' clang to work better in MacPorts case. So
 now it is better at finding the system compiler, and will also use the MP
 provided clang X.Y that the llvm X.Y corresponds to, to be used instead.
 However, this requires that clang X.Y to be available at build time, and
 as (for circular dependency reasons) cctools cannot directly depend on
 clang X.Y the logic in the gcc ports was added to make sure it is
 available, as there are in the gcc9+ builds things that cannot be built
 without a modern as.

 Now... One thing that does confuse me here is I had no problems at all
 building gcc9 or 10 with Xcode 10.2.1 on macOS10.14, with cctools
 installed with the llvm70 (and in fact llvm80) variants active. So I am
 afraid I doubt this is the (only) cause of the issues seen here. There is
 more going on to cause the build failures reported here (also note, the
 binary tarballs would also not be available if the builds with the cctools
 llvm variants where not working)....

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Ticket URL: <https://trac.macports.org/ticket/58442#comment:24>
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