[MacPorts] #58260: gcc{6, 7, 8, 9} : Build failures due to "Atomic" error with macOS 10.4.4 and Xcode 10.2

[MacPorts]

#58260: gcc{6,7,8,9} : Build failures due to "Atomic" error with macOS 10.4.4 and
Xcode 10.2
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  Reporter:  physicsbeany                        |      Owner:  (none)
      Type:  defect                              |     Status:  new
  Priority:  Normal                              |  Milestone:
 Component:  ports                               |    Version:  2.5.4
Resolution:                                      |   Keywords:  mojave
      Port:  gcc9 gcc8 gcc7 gcc6 libgcc-devel    |
  libgcc8 libgcc7 libgcc6                        |
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Comment (by ryandesign):

 Replying to [comment:6 cjones051073]:
 > I am seeing this in a number of builds on the buildbots. e.g.
 >
 >
 https://build.macports.org/builders/ports-10.14_x86_64-builder/builds/27818/steps
 /install-port/logs/stdio
 >
 > What is odd is builds that previously built fine (i.e. the binary
 tarballs exist) are now failing. This leads me to wonder if its related to
 a recent macOS/Xcode update...

 I did just update the Mojave builder to Xcode 10.2.

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Ticket URL: <https://trac.macports.org/ticket/58260#comment:16>
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