[MacPorts] #46284: Add support for universal variant to category:pure

[MacPorts]

#46284: Add support for universal variant to category:pure
----------------------------+---------------------------------
  Reporter:  aggraef@…      |      Owner:  macports-tickets@…
      Type:  defect         |     Status:  new
  Priority:  Normal         |  Milestone:
 Component:  ports          |    Version:
Resolution:                 |   Keywords:  haspatch maintainer
      Port:  category:pure  |
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Comment (by ryandesign@…):

 Thanks. I had been putting this off until someone asked for it, and here
 you are!

 We should instead default to providing a universal variant for pure module
 ports, as MacPorts does for other ports, and add `universal_variant no` to
 those that don't support it.

 The portgroup should use e.g. `[get_canonical_archflags cc]` instead of
 `${configure.universal_cflags}` (and similarly for cxxflags and ldflags)
 to avoid needing to maintain two copies of the `build.args-append`
 directive.

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Ticket URL: <https://trac.macports.org/ticket/46284#comment:1>
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