[MacPorts] #64155: bazel: builds failing for macOS 10.12 through 10.15

[MacPorts]

#64155: bazel: builds failing for macOS 10.12 through 10.15
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  Reporter:  mascguy  |      Owner:  cjones051073
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:  2.7.1
Resolution:           |   Keywords:
      Port:  bazel    |
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Comment (by cjones051073):

 Getting the bazel build to use a non-Xcode compiler has always been a huge
 headache. Honestly, I have seen these sorts of errors before but don't
 really have good suggestions as to exactly what needs to be done to help.
 The place to start is where in the Portfiles it detects its using macports
 clang, and attempts to use the `BAZEL_USE_CPP_ONLY_TOOLCHAIN=1` option...

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Ticket URL: <https://trac.macports.org/ticket/64155#comment:3>
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