[MacPorts] #54198: upgrade: port:gcc7

[MacPorts]

#54198: upgrade: port:gcc7
---------------------+----------------------
  Reporter:  RJVB    |      Owner:
      Type:  update  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:  haspatch
      Port:  gcc7    |
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Comment (by RJVB):

 RE: the with_libgcc and stub variants: a single `+single_build` variant
 might be sufficiently unambiguous to work for both subports, and also
 indicate that it is of little interest unless you're building the port
 yourself?

 One remark: I did have a single build failure yesterday, a crash of the
 cc1plus backend during (I think) the fore-last build phase. When I
 repeated the `port build` command it completed just fine so it was
 probably just a glitch, possibly due to memory pressure. (Or caused by the
 fact I added `-march=native` to configure.optflags as a reflex.)

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Ticket URL: <https://trac.macports.org/ticket/54198#comment:1>
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