[MacPorts] #55471: Use separate portindexes for libc++ on older systems

[MacPorts]

#55471: Use separate portindexes for libc++ on older systems
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  Reporter:  ryandesign   |      Owner:  neverpanic
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:  MacPorts 2.5.0
 Component:  base         |    Version:
Resolution:               |   Keywords:
      Port:               |
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Comment (by neverpanic):

 Merging https://github.com/macports/macports-base/pull/63 without the
 changes in mprsyncup will cause systems that do not get a portindex from
 the server to generate one locally. Systems won't break, but generating a
 portindex locally takes ~15 minutes on SSDs already and will be even
 slower on the typical machine still running an old setup. Since the
 portindex is first generated in the postflight of the installer, this
 leads to a bad user experience.

 Merging https://github.com/macports/macports-base/pull/83 will improve
 correctness of the server-generated portindexes when merged as-is, so we
 should probably do that. The portindex files without an explicit mention
 of C++ stdlib in its filename should always contain data for the default
 on this system, which is what PR 83 achieves. Even if we move to always
 include the C++ stdlib in the filename for all platforms later on, this
 change is correct for now.

 As such, to move the 2.5.0 release forward, I'm merging PR 83.

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Ticket URL: <https://trac.macports.org/ticket/55471#comment:32>
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