[MacPorts] #73180: Retry macOS 26 builds on buildbot with Xcode 26 Metal toolchain fix in place

[MacPorts]

#73180: Retry macOS 26 builds on buildbot with Xcode 26 Metal toolchain fix in
place
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  Reporter:  markmentovai                        |      Owner:  ryandesign
      Type:  request                             |     Status:  reopened
  Priority:  Normal                              |  Milestone:
 Component:  ports                               |    Version:
Resolution:                                      |   Keywords:
      Port:  qt6-qtwebengine, openjdk17,         |
  openjdk21, openjdk25                           |
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Comment (by ryandesign):

 On July 3 I updated that buildbot worker's macOS to 26.5.2 and Xcode and
 CLT to 26.6. I do not recall whether I reinstalled the Metal toolchain
 after that, however `xcrun metal -v` shows that it is installed and exits
 with status 0.

 Today I updated its macOS to 26.6, after which `xcrun metal -v` shows an
 error that the Metal toolchain is not installed and exits with status 1.
 After reinstalling the Metal toolchain per the wiki page, the version that
 is now installed appears to be the same as before.

 I would like to add a check to the buildbot worker startup script so that
 it does not start if the Metal toolchain is not satisfactorily installed,
 so that this problem can be detected earlier, if someone can tell me what
 command would determine that, since `xcrun metal -v` evidently isn't
 sufficient.

 Builds of the openjdk's are queued.

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Ticket URL: <https://trac.macports.org/ticket/73180#comment:51>
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