[MacPorts] #61216: Virtuoso-7 fail to install on OS 10.15 with XCode 12.0

[MacPorts]

#61216: Virtuoso-7 fail to install on OS 10.15 with XCode 12.0
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  Reporter:  JacquesLB   |      Owner:  nerdling
      Type:  defect      |     Status:  closed
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.6.3
Resolution:  fixed       |   Keywords:  xcode12
      Port:  virtuoso-7  |
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Comment (by jmroot):

 Replying to [comment:26 kencu]:
 > I believe using this fix {{{-Wno-error=implicit-function-declaration }}}
 will mean it cannot build on arm64.

 Slightly worse than that; it will build, but if there are any cases where
 the implicit declaration does not match the actual function definition,
 then incorrect machine code will be generated for the call. That will most
 likely result in mysterious incorrect runtime behaviour. You might think
 you could just trust that all the implicit declarations are correct, but
 that's unlikely to be the case because implicit declaration is always
 ambiguous. It doesn't convey whether the function takes varargs, for one
 thing, and that changes how the arguments are passed with the arm64 ABI.
 That's why Apple changed this warning to an error.

 tl;dr, if you turn off this error, you also need to disable building for
 arm64.

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Ticket URL: <https://trac.macports.org/ticket/61216#comment:27>
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